Dilute zinc alloy

Abstract

Rare zinc alloys and methods of making the same are provided. The alloy contains iron and / or copper as the main alloy metal and is prepared using hot extrusion and optionally post-extrusion annealing. The alloys exhibit high strength and improved creep resistance. The alloy is particularly suitable for the manufacture of biodegradable medical implants, although this is not unique.

Description

Technical Field

[0001] The present disclosure relates to a dilute zinc alloy and a method for manufacturing the same. The alloy exhibits high strength and improved creep resistance and is particularly suitable for the manufacture of biodegradable medical implants, although this is not the only application. Background Art

[0002] In the past few decades, zinc alloys with non-toxic compositions have received increasing attention in the manufacture of biodegradable products due to their inherent advantages in load-bearing biological applications. First, as a new class of metallic biomaterials, zinc alloys generally have better mechanical properties than their polymeric counterparts in biological scaffold applications. Second, compared with magnesium- and iron-based metallic biomaterials, zinc alloys have a moderate biodegradation rate, which can better match the healing rate of, for example, human bone. In addition, since zinc is known to be an essential element involved in nucleic acid metabolism and other basic biological processes in the human body, zinc alloys are considered to have good biocompatibility and biosafety. However, the insufficient strength and creep resistance of biocompatible zinc alloys at body temperature remain the main problems in their use in biodegradable applications.

[0003] Alloying and thermomechanical treatment are two typical methods for improving the mechanical properties of zinc alloys. However, due to the low solubility of most biocompatible elements in the zinc matrix, adding a small amount of biocompatible elements cannot effectively improve the strength of zinc alloys, while adding an excessive amount of alloying elements will lead to the formation of intermetallic compound particles, thereby reducing the strength and ductility of zinc alloys. Thermomechanical treatment of zinc alloys can improve the strength by refining the grains. However, the fine-grained microstructure in zinc alloys leads to an accelerated biological corrosion rate and creep rate at body temperature, which is harmful in biodegradable material applications.

[0004] Therefore, there is a desire to provide a zinc alloy containing a dilute amount of alloying elements and a method for manufacturing the same, in order to obtain high strength without accelerating the creep rate.

[0005] The citation of any prior art in this specification does not represent an admission or implication that such prior art constitutes a part of the common general knowledge in any jurisdiction, nor does it represent that such prior art can be reasonably understood, regarded as relevant, and / or combined with other prior art by a person skilled in the art. Summary of the Invention

[0006] On the one hand, the present disclosure provides a method for preparing a dilute zinc alloy, the method comprising the following steps:

[0007] Extruding and homogenizing a dilute zinc alloy at a temperature above 175 °C; and

[0008] Optionally, anneal the extruded dilute zinc alloy at a temperature of about 250 °C to about 400 °C;

[0009] wherein the dilute zinc alloy comprises at least 99.0 wt.% zinc; and one or both of iron and copper in a total amount of about 0.01 wt.% to about 0.99 wt.%;

[0010] wherein the dilute zinc alloy comprises one or more of magnesium, calcium, manganese, and lithium in an amount of about 0.01 wt.% to about 0.7 wt.%; and

[0011] wherein the total of iron, copper, and one or more of magnesium, calcium, manganese, and lithium does not exceed about 1.0 wt.%.

[0012] In an embodiment, the dilute zinc alloy comprises at least 99.0 wt.% zinc; and one or both of iron and copper in a total amount of about 0.03 wt.% to about 0.78 wt.%;

[0013] wherein the dilute zinc alloy comprises one or more of magnesium, calcium, manganese, and lithium in an amount of about 0.02 wt.% to about 0.7 wt.%; and

[0014] wherein the total of iron, copper, and one or more of magnesium, calcium, manganese, and lithium does not exceed 0.8 wt.%.

[0015] In an embodiment, the dilute zinc alloy comprises at least 99.0 wt.% zinc; and,

[0016] about 0.02 wt.% to about 0.97 wt.% iron and about 0.01 wt.% to about 0.1 wt.% copper, or

[0017] about 0.06 wt.% to about 0.5 wt.% copper and about 0.01 wt.% to about 0.19 wt.% iron;

[0018] wherein the dilute zinc alloy comprises one or more of magnesium, calcium, manganese, and lithium in an amount of about 0.01 wt.% to about 0.2 wt.%; and

[0019] wherein the total of iron, copper, and one or more of magnesium, calcium, manganese, and lithium does not exceed 1.0 wt.%.

[0020] In an embodiment, the dilute zinc alloy comprises at least 99.5 wt.% zinc; and,

[0021] about 0.02 wt.% to about 0.5 wt.% iron and about 0.01 wt.% to about 0.06 wt.% copper, or

[0022] about 0.06 wt.% to about 0.2 wt.% copper and about 0.01 wt.% to about 0.05 wt.% iron;

[0023] wherein the dilute zinc alloy contains one or more of magnesium, calcium, manganese, and lithium in an amount of about 0.01 wt.% to about 0.2 wt.%; and

[0024] wherein the total of iron, copper, and one or more of magnesium, calcium, manganese, and lithium does not exceed 0.5 wt.%.

[0025] In embodiments of the method, the total of iron, copper, and one or more of magnesium, calcium, manganese, and lithium does not exceed 0.7 wt.%, or 0.6 wt.%, or 0.5 wt.%, or 0.4 wt.%, or 0.3 wt.%.

[0026] In an embodiment, the dilute zinc alloy has a strong basal texture after extrusion.

[0027] In an embodiment, the dilute zinc alloy has a strong basal texture after annealing.

[0028] In an embodiment, the extrusion is performed at a temperature higher than 200 °C.

[0029] In an embodiment, the extrusion is performed at a temperature of about 200 °C to about 380 °C.

[0030] In an embodiment, the extrusion speed is about 0.01 mm.s -1 to about 10 mm.s -1 or about 0.05 mm.s -1 to about 0.5 mm . s -1 .

[0031] In an embodiment, the extrusion ratio is about 8:1 to about 80:1, or about 19:1 to about 50:1.

[0032] In an embodiment, the annealing is performed at a temperature of about 250 °C to about 350 °C.

[0033] In an embodiment, the annealing is performed for about 0.5 hour to about 50 hours, or about 1 hour to about 10 hours.

[0034] In an embodiment, the method includes a homogenization step before extrusion, wherein the dilute zinc alloy is maintained at a temperature of about 300 °C to about 400 °C. The homogenization can be carried out for a period of up to about 5 hours.

[0035] In an embodiment, the average grain size of the extruded dilute zinc alloy is greater than about 5 microns, or greater than about 10 microns.

[0036] In an embodiment, the average grain size of the extruded dilute zinc alloy is less than about 25 microns.

[0037] In an embodiment, the annealing process increases the average grain size of the dilute zinc alloy.

[0038] In an embodiment, the average grain size of the annealed dilute zinc alloy is greater than about 25 microns.

[0039] In an embodiment, the average grain size of the annealed dilute zinc alloy is from about 25 microns to about 1000 microns.

[0040] In an embodiment, the annealing process increases the ambient temperature compressive yield strength of the dilute zinc alloy.

[0041] In an embodiment, the annealing process reduces the minimum creep rate of the dilute zinc alloy.

[0042] In an embodiment of the method, the dilute zinc alloy comprises:

[0043] (a) at least 99.0 wt.% zinc;

[0044] (b) about 0.01 wt.% iron;

[0045] (c) about 0.04 wt.% copper; and

[0046] (d) about 0.05 wt.% magnesium;

[0047] or

[0048] (a) at least 99.0 wt.% zinc;

[0049] (b) about 0.06 wt.% copper; and

[0050] (c) about 0.04 wt.% magnesium;

[0051] or

[0052] (a) at least 99.0 wt.% zinc;

[0053] (b) about 0.06 wt.% iron;

[0054] (c) about 0.14 wt.% copper;

[0055] (d) about 0.01 wt.% calcium;

[0056] (e) about 0.09 wt.% manganese; and

[0057] (f) about 0.16 wt.% magnesium;

[0058] or

[0059] (a) at least 99.0 wt.% zinc;

[0060] (b) about 0.01 wt.% iron;

[0061] (c) Approximately 0.37 wt.% copper;

[0062] (d) Approximately 0.05 wt.% manganese; and

[0063] (e) Approximately 0.18 wt.% magnesium;

[0064] or

[0065] (a) At least 99.0 wt.% zinc;

[0066] (b) Approximately 0.02 wt.% iron;

[0067] (c) Approximately 0.1 wt.% copper;

[0068] (d) Approximately 0.02 wt.% calcium;

[0069] (e) Approximately 0.16 wt.% manganese; and

[0070] (f) Approximately 0.15 wt.% magnesium

[0071] or

[0072] (a) Approximately 99.6 wt.% zinc;

[0073] (b) Approximately 0.14 wt.% iron;

[0074] (c) Approximately 0.05 wt.% copper;

[0075] (d) Approximately 0.05 wt.% calcium; and

[0076] (e) Approximately 0.05 wt.% magnesium;

[0077] or

[0078] (a) Approximately 99.6 wt.% zinc;

[0079] (b) Approximately 0.14 wt.% copper;

[0080] (c) Approximately 0.03 wt.% iron;

[0081] (d) Approximately 0.05 wt.% calcium; and

[0082] (e) Approximately 0.05 wt.% magnesium.

[0083] In the examples, the dilute zinc alloy contains at least 99.1 wt.% zinc, or at least 99.2 wt.% zinc, or at least 99.3 wt.% zinc, or at least 99.4 wt.% zinc, or at least 99.5 wt.% zinc, or at least 99.6 wt.% zinc, or at least 99.7 wt.% zinc.

[0084] On the other hand, the present disclosure provides a dilute zinc alloy formed by the method according to any one of the embodiments disclosed herein.

[0085] On the other hand, the present disclosure provides a dilute zinc alloy comprising:

[0086] at least 99.0 wt.% zinc; and one or both of iron and copper in a total amount of from about 0.01 wt.% to about 0.99 wt.%;

[0087] wherein the dilute zinc alloy comprises one or more of magnesium, calcium, manganese, and lithium in an amount of from about 0.01 wt.% to about 0.7 wt.%; and

[0088] wherein the sum of iron, copper, and one or more of magnesium, calcium, manganese, and lithium does not exceed about 1.0 wt.%.

[0089] In an embodiment, the dilute zinc alloy comprises:

[0090] at least 99.0 wt.% zinc; and one or both of iron and copper in a total amount of from about 0.03 wt.% to about 0.78 wt.%;

[0091] wherein the dilute zinc alloy comprises one or more of magnesium, calcium, manganese, and lithium in an amount of from about 0.02 wt.% to about 0.7 wt.%; and

[0092] wherein the sum of iron, copper, and one or more of magnesium, calcium, manganese, and lithium does not exceed 0.8 wt.%.

[0093] In an embodiment, the dilute zinc alloy comprises:

[0094] (a) at least 99.0 wt.% zinc;

[0095] (b) from about 0.02 wt.% to about 0.97 wt.% iron and from about 0.01 wt.% to about 0.1 wt.% copper, or from about 0.06 wt.% to about 0.5 wt.% copper and from about 0.01 wt.% to about 0.19 wt.% iron;

[0096] (c) one or more of magnesium, calcium, manganese, and lithium in an amount of from about 0.01 wt.% to about 0.12 wt.%;

[0097] wherein the sum of iron, copper, and one or more of magnesium, calcium, manganese, and lithium does not exceed 1.0 wt.%.

[0098] In an embodiment, the dilute zinc alloy comprises:

[0099] (a) at least 99.5 wt.% zinc;

[0100] (b) About 0.02 wt.% to about 0.5 wt.% iron and about 0.01 wt.% to about 0.06 wt.% copper, or about 0.06 wt.% to about 0.2 wt.% copper and about 0.01 wt.% to about 0.05 wt.% iron;

[0101] (c) One or more of magnesium, calcium, manganese, and lithium in an amount of about 0.01 wt.% to about 0.12 wt.%;

[0102] Wherein the total of iron, copper, and one or more of magnesium, calcium, manganese, and lithium does not exceed 0.5 wt.%.

[0103] In an embodiment, the total of iron, copper, and one or more of magnesium, calcium, manganese, and lithium does not exceed 0.7 wt.%, or 0.6 wt.%, or 0.5 wt.%, or 0.4 wt.%, or 0.3 wt.%.

[0104] In an embodiment, the dilute zinc alloy has a strong basal texture.

[0105] In an embodiment, the average grain size of the dilute zinc alloy is greater than 5 microns, or greater than 10 microns, or greater than 25 microns.

[0106] In an embodiment, the average grain size of the dilute zinc alloy is about 5 microns to about 1000 microns.

[0107] In an embodiment, when measured at ambient temperature and a strain rate of 10 -3 s -1 the compressive yield strength of the dilute zinc alloy is greater than 220 MPa.

[0108] In an embodiment, at 37 °C under a load stress of 200 MPa, the minimum compressive creep rate of the dilute zinc alloy is less than 3×10 -6 s -1 .

[0109] In an embodiment, the dilute zinc alloy comprises:

[0110] (a) At least 99.0 wt.% zinc;

[0111] (b) About 0.01 wt.% iron;

[0112] (c) About 0.04 wt.% copper; and

[0113] (d) About 0.05 wt.% magnesium;

[0114] Or

[0115] (a) At least 99.0 wt.% zinc;

[0116] (b) About 0.06 wt.% copper; and

[0117] (c) Approximately 0.04 wt.% magnesium;

[0118] or

[0119] (a) At least 99.0 wt.% zinc;

[0120] (b) Approximately 0.06 wt.% iron;

[0121] (c) Approximately 0.14 wt.% copper;

[0122] (d) Approximately 0.01 wt.% calcium;

[0123] (e) Approximately 0.09 wt.% manganese; and

[0124] (f) Approximately 0.16 wt.% magnesium;

[0125] or

[0126] (a) At least 99.0 wt.% zinc;

[0127] (b) Approximately 0.01 wt.% iron;

[0128] (c) Approximately 0.37 wt.% copper;

[0129] (d) Approximately 0.05 wt.% manganese; and

[0130] (e) Approximately 0.18 wt.% magnesium;

[0131] or

[0132] (a) At least 99.0 wt.% zinc;

[0133] (b) Approximately 0.02 wt.% iron;

[0134] (c) Approximately 0.1 wt.% copper;

[0135] (d) Approximately 0.02 wt.% calcium;

[0136] (e) Approximately 0.16 wt.% manganese; and

[0137] (f) Approximately 0.15 wt.% magnesium;

[0138] or

[0139] (a) Approximately 99.6 wt.% zinc;

[0140] (b) Approximately 0.14 wt.% iron;

[0141] (c) Approximately 0.05 wt.% copper;

[0142] (d) Approximately 0.05 wt.% calcium; and

[0143] (e) About 0.05 wt.% magnesium;

[0144] or

[0145] (a) About 99.6 wt.% zinc;

[0146] (b) About 0.14 wt.% copper;

[0147] (c) About 0.03 wt.% iron;

[0148] (d) About 0.05 wt.% calcium; and

[0149] (e) About 0.05 wt.% magnesium.

[0150] In an embodiment, the dilute zinc alloy comprises at least 99.1 wt.% zinc, or at least 99.2 wt.% zinc, or at least 99.3 wt.% zinc, or at least 99.4 wt.% zinc, or at least 99.5 wt.% zinc, or at least 99.6 wt.% zinc, or at least 99.7 wt.% zinc.

[0151] On the other hand, the present disclosure provides an article comprising a dilute zinc alloy according to any one of the embodiments disclosed herein.

[0152] In an embodiment, the article is a medical implant.

[0153] In an embodiment, the medical implant is a stent, plate, screw, steel needle, nail or support frame.

[0154] In an embodiment, the medical implant may be a load-bearing structural implant.

[0155] In an embodiment, the medical implant may be a non-load-bearing structural implant.

[0156] Advantageously, the dilute zinc alloy of the present disclosure has a high compressive yield strength and improved creep resistance at normal human body temperature.

[0157] Advantageously, the dilute zinc alloy of the present disclosure degrades at normal human body temperature, and the daily dose of the released constituent metals is lower by several orders of magnitude than the recommended daily intake of these metals.

[0158] Furthermore, in vitro cytotoxicity tests following ISO 10993-5 (2009-06-01) and ISO 10993-12 (2012-07-01) show that cells exposed to the extracts of the dilute zinc alloy disclosed herein have no toxic reaction.

[0159] Unless otherwise explicitly stated, any embodiment herein shall be considered applicable to any other embodiment with necessary modifications.

[0160] The scope of the present disclosure is not limited by the specific embodiments described herein, which are intended for illustrative purposes only. Functionally equivalent products, compositions, and methods are clearly within the scope of the present disclosure as described herein.

[0161] Additional aspects of the present disclosure and additional embodiments of the aspects described in the foregoing paragraphs will become apparent from the following description, which is given by way of example and with reference to the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0162] Figure 1 Shown are electron backscatter diffraction (EBSD) images (left images) and particle size distributions (right images) of dilute zinc alloys prepared by hot extrusion at 250 °C and subsequent annealing treatment according to embodiments of the present disclosure; Image (a) without annealing treatment, EBSD scale 100 μm; Image (b) annealed at 275 °C, EBSD scale 100 μm; Image (c) annealed at 300 °C, EBSD scale 100 μm; Image (d) annealed at 350 °C, EBSD scale 200 μm.

[0163] Figure 2 Shown is the texture of a dilute zinc alloy prepared by hot extrusion at 250 °C and subsequent annealing treatment according to an embodiment of the present disclosure.

[0164] Figure 3 Shown is the true compressive stress-strain curve at room temperature of a dilute zinc alloy prepared by hot extrusion at 250 °C and subsequent annealing treatment according to an embodiment of the present disclosure.

[0165] Figure 4 Shown is the compressive creep curve of a dilute zinc alloy prepared by hot extrusion at 250 °C and subsequent annealing at 350 °C for 2 hours at 200 MPa at 37 °C (human body temperature) according to an embodiment of the present disclosure.

[0166] Figure 5 Shown are EBSD images (left images) and particle size distributions (right images) of dilute zinc alloys prepared by hot extrusion at 250 °C and subsequent annealing treatment according to embodiments of the present disclosure; Image (a) without annealing treatment, EBSD scale 100 μm; Image (b) annealed at 275 °C, EBSD scale 500 μm; Image (c) annealed at 300 °C, EBSD scale 500 μm; Image (d) annealed at 350 °C, EBSD scale 1000 μm.

[0167] Figure 6 Shown is the texture of a dilute zinc alloy prepared by hot extrusion at 250 °C and subsequent annealing treatment according to an embodiment of the present disclosure.

[0168] Figure 7 Shows the room-temperature true compressive stress-strain curve of a dilute zinc alloy prepared by hot extrusion at 250 °C and subsequent annealing treatment according to an embodiment of the present disclosure.

[0169] Figure 8 Shows the compressive creep curve of a dilute zinc alloy prepared by hot extrusion at 250 °C and subsequent annealing treatment at 350 °C for 2 hours at 200 MPa at 37 °C (human body temperature) according to an embodiment of the present disclosure.

[0170] Figure 9 Shows the EBSD images (left images) and grain size distributions (right images) of dilute zinc alloys prepared by hot extrusion at two extrusion temperatures of 250 °C and 300 °C and subsequent annealing treatment according to embodiments of the present disclosure; Image (a) is extruded at 250 °C without annealing treatment, EBSD scale 100 μm; Image (b) is annealed at 350 °C after extrusion at 250 °C, EBSD scale 100 μm; Image (c) is extruded at 300 °C without annealing treatment, EBSD scale 100 μm; Image (d) is annealed at 350 °C after extrusion at 300 °C, EBSD scale 500 μm.

[0171] Figure 10 Shows the texture of a dilute zinc alloy prepared by hot extrusion at two extrusion temperatures of 250 °C and 300 °C and subsequent annealing treatment according to an embodiment of the present disclosure.

[0172] Figure 11 Shows the room-temperature true compressive stress-strain curve of a dilute zinc alloy prepared by hot extrusion at two extrusion temperatures of 250 °C and 300 °C and subsequent annealing treatment according to an embodiment of the present disclosure.

[0173] Figure 12 Shows the compressive creep curve of a dilute zinc alloy prepared by hot extrusion at 250 °C and subsequent annealing treatment at 350 °C for 2 hours at 250 MPa at 37 °C (human body temperature) according to an embodiment of the present disclosure.

[0174] Figure 13Shows the EBSD images (left images) and grain size distributions (right images) of dilute zinc alloys prepared by hot extrusion at two extrusion temperatures of 250 °C and 300 °C and subsequent annealing treatment according to embodiments of the present disclosure; Image (a) is extruded at 250 °C without annealing treatment, EBSD scale 50 μm; Image (b) is annealed at 350 °C after extrusion at 250 °C, EBSD scale 200 μm; Image (c) is extruded at 300 °C without annealing treatment, EBSD scale 100 μm; Image (d) is annealed at 350 °C after extrusion at 300 °C, EBSD scale 500 μm.

[0175] Figure 14 Shows the texture of dilute zinc alloys prepared by hot extrusion at two extrusion temperatures of 250 °C and 300 °C and subsequent annealing treatment according to embodiments of the present disclosure.

[0176] Figure 15 Shows the true compressive stress-strain curves at room temperature of dilute zinc alloys prepared by hot extrusion at two extrusion temperatures of 250 °C and 300 °C and subsequent annealing treatment according to embodiments of the present disclosure.

[0177] Figure 16 Shows the compressive creep curves of a dilute zinc alloy prepared by hot extrusion at 250 °C without annealing treatment and an alloy prepared by hot extrusion at 300 °C and subsequent annealing treatment at 350 °C at 250 MPa for 2 hours at 37 °C (human body temperature).

[0178] Figure 17 Shows the EBSD images (left images) and grain size distributions (right images) of dilute zinc alloys prepared by hot extrusion at 300 °C and subsequent annealing treatment according to embodiments of the present disclosure; Image (a) without annealing treatment, EBSD scale 100 μm; Image (b) 350 °C annealing treatment for 0.5 hour, EBSD scale 100 μm; Image (c) 350 °C annealing treatment for 2 hours, EBSD scale 100 μm; Image (d) 370 °C annealing treatment for 3 hours, EBSD scale 500 μm.

[0179] Figure 18 Shows the texture of dilute zinc alloys prepared by hot extrusion at 300 °C and subsequent annealing treatment according to embodiments of the present disclosure.

[0180] Figure 19 Shows the true compressive stress-strain curves at room temperature of dilute zinc alloys prepared by hot extrusion at 300 °C and subsequent annealing treatment according to embodiments of the present disclosure.

[0181] Figure 20Shows the compressive creep curves of a dilute zinc alloy prepared by hot extrusion at 300 °C and then annealed at 370 °C for 3 hours at 250 MPa at 37 °C (human body temperature).

[0182] Figure 21 Shows that in an in vitro biodegradation test, assuming an implant surface area of 400 mm 2 , the estimated daily doses of six elements, Zn, Mg, Cu, Fe, Mn, and Ca, released from M5, M6, and M7 dilute zinc alloys. These estimated values (captured within the ellipse below) are compared with the recommended daily intake values of these six elements for different populations (captured within the ellipse above).

[0183] Figure 22 Shows the cell viability of MG-63 osteoblasts exposed to extracts of 8 different concentrations of M5, M6, and M7 dilute zinc alloys and a Mg-0.4Zn-0.1Ca alloy as a control material for 24 hours. According to ISO 10993-5 (2009-06-01), the horizontal dashed line indicates the threshold (70% cell viability) between toxic and non-toxic responses.

[0184] Figure 23 Shows the true compressive stress-strain curves at room temperature of dilute zinc alloys prepared by hot extrusion at 250 °C and 350 °C.

[0185] Figure 24 Shows the true compressive stress-strain curves at room temperature of dilute zinc alloys prepared by hot extrusion at 250 °C and 350 °C.

[0186] Figure 25 Shows the texture of (a) the dilute zinc alloy extruded at 175 °C and (b) the dilute zinc alloy prepared by hot extrusion at 175 °C and then annealed at 300 °C for 2 hours.

[0187] Figure 26 Shows the texture of (a) the dilute zinc alloy extruded at 165 °C and (b) the dilute zinc alloy prepared by hot extrusion at 165 °C and then annealed at 300 °C for 2 hours.

[0188] Figure 27 Shows the true compressive stress-strain curves at room temperature of dilute zinc alloys prepared by hot extrusion at 175 °C and then annealed.

[0189] Figure 28 Shows the true compressive stress-strain curves at room temperature of dilute zinc alloys prepared by hot extrusion at 165 °C and then annealed.

[0190] Figure 29Shows the compression creep curves of the comparative Mg-0.4Zn-0.1Ca alloy prepared by hot extrusion at 250 MPa at 220 °C or 400 °C at 37 °C.

[0191] Figure 30 Shows the EBSD images (left image) and grain size distributions (right image) of pure zinc prepared by hot extrusion at 150 °C and subsequent annealing treatment; Image (a) without annealing treatment, EBSD scale 200 μm; Image (b) annealed at 200 °C for 0.5 h, EBSD scale 200 μm.

[0192] Figure 31 Shows the texture of pure zinc prepared by hot extrusion at 150 °C and subsequent annealing treatment.

[0193] Figure 32 Shows the true compression stress-strain curve at room temperature of pure zinc prepared by hot extrusion at 150 °C (compressive yield strength = 74 MPa) and subsequent annealing treatment (compressive yield strength = 132 MPa). Detailed Description

[0194] It should be understood that the present disclosure described and defined in this specification extends to all alternative combinations of two or more features mentioned or apparent in the text or drawings. All such different combinations constitute various alternative aspects of the present disclosure.

[0195] Definitions

[0196] For the purposes of interpreting this specification, the terms used in the singular shall also include the plural and vice versa.

[0197] As used herein, unless the context requires otherwise, the term "comprise" and variations of the term, such as "comprising", "comprises" and "comprised", are not intended to exclude additional additions, components, wholes or steps.

[0198] When referring to measurable values such as amounts, durations, etc., the term "about" as used herein means encompassing a deviation of ±20% or ±10% from the specified value, in some embodiments ±5%, in some embodiments ±1%, and in some embodiments ±0.1%, as such deviations are suitable for carrying out the disclosed methods.

[0199] Scope: Throughout this disclosure, various aspects of the invention may be presented in a range format. It should be understood that the description in range format is for convenience and brevity only and should not be construed as a rigid limitation on the scope of the invention. Accordingly, the description of a range should be considered to have specifically disclosed all possible sub-ranges as well as the individual numerical values within that range. For example, a description of a range such as 1 to 6 should be considered to have specifically disclosed sub-ranges such as 1 to 3, 1 to 4, 1 to 5, 2 to 4, 2 to 6, 3 to 6, etc., as well as the individual numbers within that range, e.g., 1, 2, 2.7, 3, 4, 5, 5.3, 6. This applies regardless of how broad the range is.

[0200] As used herein, the term "strong basal texture" with respect to a metal alloy means that the c-axes of most of the grains in the metal alloy are perpendicular to the extrusion direction.

[0201] This disclosure relates to novel dilute zinc alloys and methods for their manufacture.

[0202] This disclosure provides biodegradable zinc alloys with selected alloying elements added in dilution and methods for their manufacture. The dilute zinc alloys have high compressive yield strength and improved creep resistance. These methods involve extrusion under specific processing conditions and optionally post-extrusion annealing of the resulting specific microstructure. The stronger and more creep-resistant zinc alloys according to this disclosure contain iron and / or copper, where the total amount of added alloying elements is less than 1.0 wt.%, and the balance is zinc and unavoidable impurity elements (the total content of impurity elements is generally less than 0.06 wt.% and the content of a single impurity element is generally less than 0.016 wt.%). These alloys are hot-extruded at a suitable extrusion ratio and speed at a temperature above 175 °C to obtain a strong basal texture, and optionally subsequently annealed at a temperature of 250 - 400 °C. The compressive yield strength of the alloy increases with increasing grain size, which is caused by post-extrusion annealing at high temperature or a suitable combination of extrusion parameters, contrary to the conventional annealing softening behavior of metals or the traditional view that the strength of metals with increasing grain size will decrease.

[0203] Preparation method

[0204] In one aspect, there is provided a method for preparing a dilute zinc alloy, the method comprising the steps of:

[0205] extruding a homogenized dilute zinc alloy at a temperature above 175 °C; and

[0206] optionally annealing the extruded dilute zinc alloy at a temperature of about 250 °C to about 400 °C;

[0207] wherein the dilute zinc alloy comprises at least 99.0 wt.% zinc; and one or both of iron and copper in a total amount of about 0.01 wt.% to about 0.99 wt.%;

[0208] wherein the dilute zinc alloy comprises one or more of magnesium, calcium, manganese, and lithium in an amount of from about 0.01 wt.% to about 0.7 wt.%; and

[0209] wherein the sum of iron, copper, and one or more of magnesium, calcium, manganese, and lithium does not exceed about 1.0 wt.%.

[0210] Without being bound by theory, an important effect of hot extrusion is to obtain a fully recrystallized microstructure having a strong basal texture to allow intergranular deformation to be the primary deformation mode during plastic deformation. Control of this intergranular deformation mode may be important for annealing hardening that occurs in such dilute alloys or even pure zinc. This is in contrast to conventional methods that involve control of intragranular deformation modes (dislocation slip or twinning), where the compressive strength decreases with increasing grain size, following the conventional Hall-Petch relationship and the well-known annealing softening phenomenon.

[0211] The manufacturing method disclosed herein may include only extrusion, i.e., no post-extrusion annealing. In such extrusion, a combination of extrusion parameters such as temperature, speed, and ratio results in an extruded microstructure that is fully recrystallized and has a strong basal texture and a relatively large grain size.

[0212] In an embodiment, a zinc alloy is prepared by casting, the zinc alloy comprising alloying elements added in a total percentage not exceeding 1.0 wt.%, including iron, copper, calcium, magnesium, manganese, and lithium, with the balance being zinc and unavoidable impurities.

[0213] In an embodiment, the cast alloy is homogenized at about 350 °C for 2 hours, followed by hot extrusion. To obtain a strong basal texture and a fully recrystallized microstructure in the extruded state, the extrusion temperature is controlled above 175 °C, and the extrusion ratio is controlled in the range of 19:1 - 50:1.

[0214] Subsequently, the extrudate is optionally subjected to a post-extrusion annealing treatment at a temperature in the range of about 250 °C to about 400 °C. Compared to the extruded samples, the samples subjected to post-extrusion annealing exhibit a higher compressive yield strength, which increases with increasing annealing temperature, and improved creep resistance at body temperature.

[0215] It is well known that the strength and other mechanical properties of zinc alloys are highly correlated with the alloy microstructure and texture. The present inventors have found that only zinc alloy samples with a strong basal texture exhibit annealing strengthening, while zinc alloy samples with a non-basal texture exhibit conventional annealing softening behavior during uniaxial compressive deformation at room temperature. Without being bound by theory, the reason why zinc alloys with a strong basal texture are strengthened by annealing is that during the deformation of the alloy, the loading direction is almost parallel to the basal planes of most grains, thus suppressing the basal slip that is most easily activated and operative. Since zinc has a relatively high homologous temperature at room temperature, i.e., T / T m = 0.4, during plastic deformation at room temperature, creep-based intergranular deformation may alternatively occur. However, the ease of intergranular deformation decreases with increasing grain size, and non-basal slip modes with higher activation stresses must be activated and operative in coarse-grained samples to contribute to plastic strain. Therefore, the compressive strength of annealed samples with relatively large grains is higher than that of extruded samples with relatively small grains. In contrast, during the compressive deformation of zinc alloy samples with a non-basal texture, basal slip dominates in all samples regardless of grain size, and its compressive yield strength decreases with increasing grain size.

[0216] By applying hot extrusion under various conditions, the microstructure and texture of zinc alloys can be effectively changed. In this article, the extrusion temperature is the main factor affecting the texture and recrystallization fraction in the extruded zinc alloy. For example, when dilute zinc alloys are extruded at a temperature of 175 °C or lower, the extruded samples exhibit a partially recrystallized microstructure and a weak non-basal texture, and the non-basal texture is strengthened by post-extrusion annealing of the extruded samples. In contrast, as the extrusion temperature increases above 175 °C, the extruded samples have a fully recrystallized microstructure and a strong basal texture, and the basal texture is retained after post-extrusion annealing.

[0217] In an embodiment, the extrusion is performed at a temperature higher than 175 °C, or higher than about 180 °C, or higher than about 190 °C, or higher than about 200 °C, or higher than about 210 °C, or higher than about 220 °C, or higher than about 230 °C, or higher than about 240 °C.

[0218] In an embodiment, the extrusion is performed at a temperature of about 180 °C to about 380 °C, or about 180 °C to about 350 °C, or about 180 °C to about 300 °C, or about 180 °C to about 270 °C, or about 180 °C to about 260 °C, or about 180 °C to about 250 °C, or about 200 °C to about 280 °C, or about 200 °C to about 270 °C, or about 200 °C to about 260 °C, or about 200 °C to about 250 °C.

[0219] In an embodiment, the extrusion speed is about 0.01 mm .s -1 from about 10 mm . s -1 to about 0.05 mm . s -1 to about 5 mm.s -1 or about 0.05 mm.s -1 to about 1 mm.s -1 or about 0.05 mm.s -1 to about 0.5 mm.s -1 or about 0.05 mm.s -1 to about 0.4 mm.s -1 or about 0.05 mm.s -1 to about 0.3 mm.s -1 or about 0.05 mm . s -1 to about 0.2 mm . s -1 .

[0220] In an embodiment, the extrusion ratio is from about 8:1 to about 80:1, or from about 19:1 to about 60:1, or from about 19:1 to about 50:1, or from about 19:1 to about 45:1, or from about 25:1 to about 45:1, or from about 30:1 to about 40:1.

[0221] In an embodiment, annealing is performed at a temperature of from about 250 °C to about 400 °C, or from about 250 °C to about 375 °C, or from about 275 °C to about 400 °C, or from about 275 °C to about 375 °C.

[0222] In an embodiment, the annealing is performed for about 0.5 hour to about 50 hours, or about 1 hour to about 10 hours, or about 1 hour to about 5 hours.

[0223] In an embodiment, the average grain size of the extruded alloy is greater than about 5 microns, or greater than about 6 microns, or greater than about 7 microns, or greater than about 8 microns, or greater than about 9 microns, or greater than about 10 microns.

[0224] In an embodiment, the average grain size of the extruded alloy is less than about 25 microns, or from about 5 microns to about 25 microns.

[0225] In an embodiment, the annealing process increases the average grain size of the alloy.

[0226] In an embodiment, the average grain size of the annealed alloy is greater than about 25 microns, or greater than about 30 microns, or greater than about 40 microns, or greater than about 50 microns, or greater than about 60 microns, or greater than about 70 microns, or greater than about 80 microns.

[0227] In an embodiment, the average grain size of the annealed alloy is from about 25 microns to about 1000 microns, or from about 25 microns to about 1000 microns, or from about 25 microns to about 800 microns, or from about 25 microns to about 600 microns, or from about 25 microns to about 400 microns, or from about 25 microns to about 200 microns.

[0228] In a specific embodiment, the selected alloying element is added in a dilution amount (equal to or less than 1.0 wt.%), and extrusion parameters such as temperature, ratio, and speed are such that the extruded sample has a strong basal texture and a fully recrystallized microstructure. The extrusion temperature is controlled above 175 °C, and the extrusion ratio is controlled in the range of 19:1 - 50:1 to obtain an extruded sample with a strong basal texture and a fully recrystallized microstructure. The speed of the extrusion pusher is relatively low, such as 0.05 mm·s -1 to 0.5 mm·s -1 to obtain a good surface finish of the extrusion rod.

[0229] In an embodiment, the annealing process increases the ambient temperature compressive strength of the alloy.

[0230] In an embodiment, the annealing process reduces the minimum creep rate of the alloy. In some embodiments, the annealing process reduces the minimum creep rate of the alloy by 2 times, or 3 times, or 4 times, or 5 times, or 6 times, or 7 times, or 8 times, or 9 times, or 10 times.

[0231] Alloy composition

[0232] The dilute zinc alloy of the present disclosure comprises at least 99.0 wt.% zinc;

[0233] one or both of iron and copper in a total amount of from about 0.01 wt.% to about 0.99 wt.%;

[0234] one or more of magnesium, calcium, manganese, and lithium in an amount of from about 0.01 wt.% to about 0.7 wt.%; and

[0235] the sum of iron, copper, and one or more of magnesium, calcium, manganese, and lithium does not exceed about 1.0 wt.%.

[0236] In an embodiment, the dilute zinc alloy comprises at least 99.1 wt.% zinc, or at least 99.2 wt.% zinc, or at least 99.3 wt.% zinc, or at least 99.4 wt.% zinc, or at least 99.5 wt.% zinc, or at least 99.6 wt.% zinc, or at least 99.7 wt.% zinc.

[0237] In some embodiments, the dilute zinc alloy comprises from about 0.01 wt.% to about 0.90 wt.% iron, or from about 0.01 wt.% to about 0.80 wt.% iron, or from about 0.01 wt.% to about 0.70 wt.% iron, or from about 0.01 wt.% to about 0.60 wt.% iron, or from about 0.01 wt.% to about 0.50 wt.% iron, or from about 0.01 wt.% to about 0.40 wt.% iron, or from about 0.01 wt.% to about 0.30 wt.% iron, or from about 0.01 wt.% to about 0.20 wt.% iron, or from about 0.01 wt.% to about 0.10 wt.% iron, or from about 0.01 wt.% to about 0.05 wt.% iron.

[0238] In some embodiments, the dilute zinc alloy comprises from about 0.01 wt.% to about 0.90 wt.% copper, or from about 0.01 wt.% to about 0.80 wt.% copper, or from about 0.01 wt.% to about 0.70 wt.% copper, or from about 0.01 wt.% to about 0.60 wt.% copper, or from about 0.01 wt.% to about 0.50 wt.% copper, or from about 0.01 wt.% to about 0.40 wt.% copper, or from about 0.01 wt.% to about 0.30 wt.% copper, or from about 0.01 wt.% to about 0.20 wt.% copper, or from about 0.01 wt.% to about 0.10 wt.% copper, or from about 0.01 wt.% to about 0.05 wt.% copper.

[0239] In some embodiments, the dilute zinc alloy comprises one or both of from about 0.01 wt.% to about 0.90 wt.% of iron and copper, or one or both of from about 0.01 wt.% to about 0.80 wt.% of iron and copper, or one or both of from about 0.01 wt.% to about 0.70 wt.% of iron and copper, or one or both of from about 0.01 wt.% to about 0.60 wt.% of iron and copper, or one or both of from about 0.01 wt.% to about 0.50 wt.% of iron and copper, or one or both of from about 0.01 wt.% to about 0.40 wt.% of iron and copper, or one or both of from about 0.01 wt.% to about 0.30 wt.% of iron and copper, or one or both of from about 0.01 wt.% to about 0.20 wt.% of iron and copper, or one or both of from about 0.01 wt.% to about 0.10 wt.% of iron and copper, or one or both of from about 0.01 wt.% to about 0.05 wt.% of iron and copper.

[0240] In some preferred embodiments, the dilute zinc alloy comprises one or both of from about 0.02 wt.% to about 0.60 wt.% of iron and copper.

[0241] In some embodiments, the dilute zinc alloy comprises one or more of magnesium, calcium, manganese, and lithium in an amount of about 0.01 wt.% to about 0.70 wt.%, or about 0.01 wt.% to about 0.60 wt.%, or about 0.01 wt.% to about 0.50 wt.%, or about 0.01 wt.% to about 0.40 wt.%, or about 0.02 wt.% to about 0.50 wt.%, or about 0.02 wt.% to about 0.40 wt.%.

[0242] In embodiments, the total amount of iron, copper, magnesium, calcium, manganese, and lithium in the dilute zinc alloy is about 0.05 wt.% to about 1.0 wt.%, or about 0.05 wt.% to about 0.9 wt.%, or about 0.05 wt.% to about 0.8 wt.%, or about 0.05 wt.% to about 0.7 wt.%.

[0243] In some preferred embodiments, the dilute zinc alloy comprises about 99.1 wt.% to about 99.95 wt.% zinc, one or both of iron and copper in an amount of about 0.01 wt.% to about 0.90 wt.%, and one or more of magnesium, calcium, manganese, and lithium in an amount of about 0.01 wt.% to about 0.70 wt.%.

[0244] In embodiments, when measured at ambient temperature and a strain rate of 10 -3 s -1 the compressive yield strength of the alloy is greater than 220 MPa, or greater than 230 MPa, or greater than 240 MPa, or greater than 250 MPa, or greater than 260 MPa, or greater than 270 MPa, or greater than 280 MPa, or greater than 290 MPa, or greater than 300 MPa.

[0245] In embodiments, the minimum compression creep rate of the alloy is less than 3×10 -6 s -1 at 37 °C under a load stress of 200 MPa, or less than 2×10 -6 s -1 or less than 1×10 -6 s -1 or less than 5×10 -7 s -1 or less than 3×10 -7 s -1 or less than 2×10 -7 s -1 or less than 1×10 -7 s -1 .

[0246] Embodiments

[0247] Analysis techniques

[0248] The composition of the metal alloy was determined by inductively coupled plasma atomic emission spectrometry (ICP-AES).

[0249] EBSD characterization was carried out on a JEOL JSM-7001F FEG SEM equipped with a Nordlys Max 2 EBSD detector. Oxford Instruments' Aztec software was used as the acquisition system to control data processing, and post-data analysis, including EBSD orientation mapping, grain size measurement, and inverse pole figure plotting, was performed on Channel 5HKL software.

[0250] Uniaxial compression and tensile tests were carried out using an Instron 5982 machine, which has a fixed load cell of 100 kN and is controlled by 2 software. According to the ASTM E9-09(2009) standard, cylindrical compression specimens with a diameter of 6 mm and a height of 9 mm were machined along the ED, and the standard height-to-diameter ratio was 1.5:1. The compression test was carried out at a crosshead speed of 0.54 mm min -1 (corresponding to a strain rate of 10 -3 s -1 ). Circular dog-bone tensile specimens with a gauge length of 15 mm and a gauge diameter of 3.5 mm were machined along the ED for tensile tests. The dimensions of the tensile specimens followed the ASTM E8M(2013) standard. A clip-on extensometer with a gauge length of 10 mm was used for the tensile test, and the crosshead speed was 0.9 mm min -1 (corresponding to a strain rate of 10 -3 s -1 ).

[0251] A constant-load compression creep test was carried out on an Instron 5982 machine equipped with two hair dryers for temperature control, and a thermometer was set up to measure the surface temperature of the specimen. According to the ASTM E9-09(2009) standard, cylindrical compression specimens with a diameter of 6 mm and a height of 9 mm were machined along the ED, and the standard height-to-diameter ratio was 1.5:1. Before the creep test, the specimen was heated at 37 °C for 10 minutes, and the temperature fluctuated within ±1 °C. During the creep test, the specimen was tested at a constant stress of 200 MPa or 250 MPa until it was manually stopped after 2 hours. Creep data were collected using 2 software.

[0252] Alloy preparation and processing

[0253] The purities of the metals were: Zn (99.95%), Fe (99.98%), Cu (99.99%), Ca (99%), and Mg (99.95%).

[0254] The dilute zinc alloy was prepared by induction melting in a graphite crucible at about 550 °C under an argon atmosphere. The molten alloy was then cast into a preheated steel mold coated with boron nitride (∼150 °C), and subsequently cooled naturally to room temperature. The cast ingot was a cylinder weighing about 1 kg and having dimensions of 38 mm in diameter and 140 mm in length. A cylindrical blank with dimensions of Φ35×60 mm 3 was machined from the cast ingot for subsequent homogenization, hot extrusion, and post-extrusion annealing treatments. Table 1 summarizes the alloy composition. Before hot extrusion, the machined billet was homogenized by heat treatment in a muffle furnace at 300 °C for 2 hours, followed by water quenching, and then extruded into a cylindrical rod with a diameter of 6 mm at a ram speed of 0.1 mm s -1 (corresponding to an extrusion ratio of about 36:1). During the extrusion process, all billets were preheated at their extrusion temperature for 10 minutes, and the extruded parts were directly quenched in water at room temperature. The post-extrusion annealing heat treatment was carried out in a muffle furnace, followed by water quenching.

[0255]

[0256] Example 1: Annealing Strengthening of M3 Alloy

[0257] The cast M3 alloy was homogenized at 300 °C for 2 hours, followed by water quenching. The homogenized billet was extruded into a cylindrical rod with a diameter of 6 mm at a ram speed of 0.1 mm·s -1 at temperatures above 175 °C. The extrusion ratio was controlled to be about 36:1. After hot extrusion, annealing treatments were carried out at temperatures of 275 °C, 300 °C, and 350 °C for 2 hours. Table 2 summarizes the conditions of extrusion and post-extrusion annealing (if performed).

[0258]

[0259]

[0260] As shown in Table 3, various extrusion and post-extrusion annealing conditions produced different grain sizes ranging from 11 μm to 95 μm.

[0261]

[0262] Figure 1 The microstructures (left images) and grain size distributions (right images) of the M3 alloy are shown for (a) 250E, (b) 250E + 275 °C / 2 h, (c) 250E + 300 °C / 2 h, and (d) 250E + 350 °C / 2 h, respectively. Figure 2 The textures of four identical samples are shown.

[0263] At room temperature and a strain rate of 10 -3 s -1 , uniaxial compression deformation was carried out on the extruded and annealed samples along the extrusion direction. The true stress-strain curves are shown in Figure 3 , and the compressive yield strength values are listed in Table 3. The compressive yield strength of the extruded alloy (250E) was 277 MPa, lower than that of all annealed alloys. Its compressive strength increased with the increase of the annealing temperature. The compressive yield strength of the 250E + 275 °C / 2 h sample was 285 MPa, the compressive yield strength of the 250E + 300 °C / 2 h sample was 290 MPa, and the compressive yield strength of the 250E + 350 °C / 2 h sample was 305 MPa. Annealing after extrusion at 350 °C for 2 h provided the greatest strength improvement for the extruded M3 alloy. A compression creep test was carried out on the M3 alloy extruded at 250 °C and then annealed at 350 °C for 2 h under a load stress of 200 MPa at 37 °C. The creep curves are shown in Figure 4 , and the minimum creep rates are listed in Table 3. For the M3 alloy extruded at 250 °C, the sample annealed at 350 °C for 2 h had the minimum creep rate (2.5×10 -7 s -1 ), which was ten times lower than that of the extruded sample, indicating that the annealing treatment after extrusion effectively improved the creep resistance of the M3 alloy.

[0264] Example 2: Annealing Strengthening of M4 Alloy

[0265] The cast M4 alloy was homogenized at 300 °C for 2 h and then water quenched. The homogenized billet was extruded into a cylindrical rod with a diameter of 6 mm at a pusher speed of 0.1 mm·s -1 at a temperature above 200 °C. The extrusion ratio was controlled to be about 36:1. After hot extrusion, annealing treatments were carried out at 275 °C, 300 °C and 350 °C for 2 h. Table 4 summarizes the conditions of extrusion and annealing after extrusion (if carried out).

[0266]

[0267] The extruded rod had a fully recrystallized microstructure and a strong basal texture. As shown in Table 5, various extrusion and annealing-after-extrusion conditions produced different grain sizes ranging from about 22 μm to about 630 μm.

[0268]

[0269] Figure 5Shows the microstructure (left image) and grain size distribution (right image) of M4 alloy at (a) 250E, (b) 250E + 275 °C / 2 h, (c) 250E + 300 °C / 2 h, and (d) 250E + 350 °C / 2 h, respectively. As Figure 6 shown by the corresponding inverse pole figures in

[0270] Uniaxial compressive deformation was carried out along the extrusion direction at room temperature and a strain rate of 10 -3 s -1 . The obtained true stress-strain curves are shown in Figure 7 , and the compressive yield strength values of the extruded and annealed M4 alloy samples are listed in Table 5. The lowest compressive yield strength of the 250 °C extruded alloy sample with an average grain size of about 22 μm is 250 MPa. With the increase in grain size, the compressive yield strengths of the 250E + 275 °C / 5 h (55 μm), 250E + 300 °C / 2 h (88 μm), and 250E + 350 °C / 24 h (630 μm) samples are 277 MPa, 308 MPa, and 321 MPa, respectively. The compression creep tests of the M4 alloy samples under the conditions of 250E and 250E + 350 °C / 2 h were carried out at 37 °C (human body temperature) under a load stress of 200 MPa. The creep curves are shown in Figure 8 , and the minimum creep rates are listed in Table 5. Applying extrusion and annealing at 350 °C for 2 h increased the creep resistance of the M4 alloy extruded at 250 °C by about an order of magnitude.

[0271] Example 3: Influence of Load Direction on Annealing Strengthening Response of M3 and M4 Alloys

[0272] The influence of the load direction on the annealing strengthening response of M3 and M4 alloys was studied. Uniaxial tensile deformation of M3 and M4 alloys extruded at 250 °C and subsequently annealed at 300 °C for 2 h was carried out at room temperature and a strain rate of 10 -3 s -1 , and the load direction was parallel to the extrusion direction. The tensile yield strength values (tensile YS) are listed in Tables 3 and 5. For the M3 and M4 alloys extruded at 250 °C, the annealing strengthening response observed in the uniaxial compression test does not exist in the tensile deformation.

[0273] Example 4: Annealing Strength of M5 Alloy

[0274] The cast M5 alloy was homogenized at 300 °C for 2 h and then water quenched. At a temperature above 200 °C at 0.1 mm·s -1The pusher speed extruded the homogenized billet into a cylindrical rod with a diameter of 6 mm. The extrusion ratio was controlled to be about 36:1. After hot extrusion, an annealing treatment was carried out at a temperature of 350 °C for 2 hours. Table 6 summarizes the conditions of extrusion and post-extrusion annealing (if performed).

[0275]

[0276] The extruded rods had a fully recrystallized microstructure and a strong basal texture. As shown in Table 7, various extrusion and post-extrusion annealing conditions produced different grain sizes ranging from about 12 μm to about 129 μm.

[0277]

[0278]

[0279] Figure 9 The microstructure (left image) and grain size distribution (right image) of the M5 alloy are shown for (a) 250E, (b) 250E + 350 °C / 2 h, (c) 300E, and (d) 300E + 350 °C / 2 h, respectively. As Figure 10 shown in the corresponding inverse pole figures, the basal texture formed during extrusion and remained after the annealing treatment.

[0280] At room temperature and a strain rate of 10 -3 s -1 uniaxial compressive deformation was carried out along the extrusion direction. The obtained true stress-strain curves are shown in Figure 11 and the compressive yield strength values of the extruded and annealed M5 alloy samples are listed in Table 7. The lowest compressive yield strength of the 250 °C extruded alloy sample with an average grain size of about 12 μm was 350 MPa. As the grain size increased, the compressive yield strengths of the 300E (16 μm), 250E + 350 °C / 2 h (32 μm), and 300E + 350 °C / 2 h (129 μm) samples were 359 MPa, 360 MPa, and 381 MPa, respectively. The compression creep tests of the M5 alloy samples under the conditions of 250E and 250E + 350 °C / 2 h were carried out at 37 °C (human body temperature) under a load stress of 250 MPa. The creep curves are shown in Figure 12 and the minimum creep rates are listed in Table 7. Applying post-extrusion annealing at 350 °C for 2 hours improved the creep resistance of the M5 alloy extruded at 250 °C by more than an order of magnitude.

[0281] Example 5: Annealing Strength of M6 Alloy

[0282] The cast M6 alloy was homogenized at 300 °C for 2 hours and then water quenched. At a temperature above 200 °C at 0.1 mm·s-1 The pusher speed extruded the homogenized billet into a cylindrical rod with a diameter of 6 mm. The extrusion ratio was controlled to be approximately 36:1. After hot extrusion, annealing treatments were carried out at a temperature of 350 °C for 2 hours and 6 hours. Table 8 summarizes the conditions of extrusion and post-extrusion annealing (if carried out).

[0283]

[0284]

[0285] The extruded rods had a fully recrystallized microstructure and a strong basal texture. As shown in Table 9, various extrusion and post-extrusion annealing conditions produced different grain sizes from approximately 8 μm to approximately 208 μm.

[0286]

[0287] Figure 13 Showed the microstructure (left image) and grain size distribution (right image) of the M6 alloy, which were (a) 250E, (b) 250E + 350 °C / 6 h, (c) 300E, and (d) 300E + 350 °C / 2 h, respectively. As Figure 14 shown in the corresponding inverse pole figure in, the basal texture formed during the extrusion process and was retained after the annealing treatment.

[0288] At room temperature and a strain rate of 10 -3 s -1 uniaxial compressive deformation was carried out along the extrusion direction. The obtained true stress-strain curves were shown in Figure 15 and the compressive yield strength values of the extruded and annealed M6 alloy samples were listed in Table 9. The lowest compressive yield strength of the 250 °C extruded alloy sample with an average grain size of approximately 8 μm was 326 MPa. As the grain size increased, the compressive yield strengths of the 300E (23 μm), 250E + 350 °C / 6 h (43 μm), and 300E + 350 °C / 2 h (208 μm) samples were 355 MPa, 386 MPa, and 398 MPa, respectively. The compression creep tests of the M6 alloy samples under the conditions of 250E and 300E + 350 °C / 2 h were carried out at 37 °C (human body temperature) under a load stress of 250 MPa. The creep curves were shown in Figure 16 and the minimum creep rates were listed in Table 9. Compared with the samples extruded at 250 °C, the M6 alloy extruded at 300 °C and then subjected to 2 hours of post-extrusion annealing at 350 °C showed more than an order of magnitude improvement in creep resistance.

[0289] Example 6: Annealing Strength of M7 Alloy

[0290] The as-cast M7 alloy was homogenized at 300 °C for 2 h and then quenched in water. The homogenized billet was extruded into a cylindrical rod with a diameter of 6 mm at a ram speed of 0.1 mm·s -1 at a temperature above 300 °C. The extrusion ratio was controlled to be approximately 36:1. After hot extrusion, annealing treatments were carried out at temperatures of 350 °C and 370 °C for variable durations between 0.5 h and 3 h. Table 10 summarizes the conditions of extrusion and post-extrusion annealing (if performed).

[0291]

[0292] The extruded rods had a fully recrystallized microstructure and a strong basal texture. As shown in Table 11, various extrusion and post-extrusion annealing conditions produced different grain sizes ranging from approximately 21 μm to approximately 65 μm.

[0293]

[0294] Figure 17 The microstructure (left image) and grain size distribution (right image) of the M7 alloy are shown for (a) 300E, (b) 300E + 350 °C / 0.5 h, (c) 300E + 350 °C / 2 h, and (d) 300E + 370 °C / 3 h, respectively. As shown in the corresponding inverse pole figures in Figure 18 , the basal texture was retained after the annealing treatment.

[0295] Uniaxial compressive deformation was carried out along the extrusion direction at room temperature and a strain rate of 10 -3 s -1 . The obtained true stress-strain curves are shown in Figure 19 , and the compressive yield strength values of the extruded and annealed M7 alloy samples are listed in Table 11. The lowest compressive yield strength of the 300 °C extruded alloy sample with an average grain size of approximately 21 μm was 365 MPa. With the increase in grain size, the compressive yield strengths of the 300E + 350 °C / 0.5 h (28 μm), 300E + 350 °C / 2 h (32 μm), and 300E + 370 °C / 3 h (65 μm) samples were 394 MPa, 406 MPa, and 433 MPa, respectively. Compression creep tests of the M7 alloy samples under the conditions of 300E and 300E + 370 °C / 3 h were carried out at 37 °C (human body temperature) under a load stress of 250 MPa. The creep curves are shown in Figure 20 , and the minimum creep rates are listed in Table 11. Applying post-extrusion annealing at 370 °C for 3 h improved the creep resistance of the M7 alloy extruded at 300 °C by approximately one order of magnitude.

[0296] Example 7: In vitro biodegradation test

[0297] The biocorrosion rate of zinc alloy samples was determined by immersion tests. Samples with a diameter of 6 mm and a thickness of 1 mm were ground and polished with 1 μm diamond suspension, weighed, ultrasonically treated in ethanol, and immersed in Dulbecco's Modified Eagle Medium (DMEM, Gibco, ThermoFisher Scientific Australia) at 37 °C and in a 5% CO2 atmosphere for 30 days. The ratio of the solution volume to the sample surface area (V / S) was 0.4 mL / mm 2 , as directed by ASTM-G31-72 (1972). The DMEM solution was renewed every 48 hours. After the immersion test, the corroded samples were treated with a solution containing 200 g / L CrO3 and 10 g / L AgNO3 for 15 minutes to remove the corrosion products. The biocorrosion rate of each sample was calculated based on the weight loss measured after 30 days of immersion according to the formula outlined in ASTM-G31-72 (1972): Corrosion rate = (K × 2) / (A × T × ρ), where K is a constant (8.76 × 10 4 , in units of mm / year), W is the weight loss in grams, A is the exposed sample surface area in cm 2 , T is the exposure time in hours, and ρ is the sample density in g / cm 3 .

[0298] Figure 21 shows the estimated daily doses (data points contained in the ellipse below) of six elements, Zn, Mg, Cu, Fe, Mn, and Ca, released from alloys M5, M6, and M7, assuming an implant surface area of 400 mm 2 . These estimated values were compared with the recommended daily intake values (data points in the ellipse above) of these six elements for different populations. Apparently, the estimated daily doses released from the alloys are several orders of magnitude lower than the recommended daily intake values.

[0299] Example 8: Cell viability study

[0300] MG-63( CRL-1427 TM ) human osteosarcoma cell line, which maintains the form of human pre-osteoblasts and has behavior similar to immature in vivo osteoblasts at an early differentiation stage, was used for the indirect contact cell viability test. These tests employed 3-(4,5-Dimethylthiazol-2-yl)-5-(3-carboxymethoxyphenyl)-2-(4-sulfophenyl)-2H-tetrazolium inner salt (MTS, Cell Titre Aqueous single-solution cell proliferation assay was performed by Promega, Australia. Control samples and dilute magnesium alloy (Mg-0.4Zn-0.1Ca) extruded at 400 °C (see Example 11) were used for comparison. The sample sterilization procedure involved disk samples approximately 1 mm thick, which were polished with 1 μm diamond suspension, ultrasonically treated in ethanol for at least 30 minutes, and then exposed to UV light for 20 minutes (10 minutes on each side). The samples were then placed in an antimicrobial solution of 1 vol.% penicillin / streptomycin (Gibco, Thermo Fisher Scientific Australia) and 99 vol.% sterile phosphate-buffered saline (PBS) at 4 °C for 1 hour, followed by washing in sterile PBS on a plate shaker for five cycles.

[0301] MG-63 cells were cultured in low-glucose (1 g / L) DMEM supplemented with 1 vol.% penicillin / streptomycin and 10 vol.% fetal bovine serum (FBS, Gibco, Thermo Fisher Scientific Australia) in an incubator at 37 °C, 5% CO2, and 95% humidity. MG-63 cells within the P5 - P10 passage range were selected for the indirect MTS assay.

[0302] Cytotoxicity assessment was carried out according to ISO 10993-5 (2009-06-01) / ISO 10993-12 (2012-07-01). On day 0, cells were seeded at a density of 10 4 cells / cm 2 in 96-well plates and incubated for 24 hours to promote cell attachment. According to ISO 10993-12 (2012-07-01), extracts were prepared by immersing the samples in cell culture medium for 24 hours at 37 °C in an environment of 5% CO2 and 95% humidity, with the ratio of the surface area of the sample to the medium being 1.25 mL / cm 2 . On day 1, the cell culture medium was replaced with 100 μL / well of sample extracts at 8 different concentrations (100%, 50%, 25%, 12.5%, 6.25%, 3.125%, 1.56%, and 0.78%), and incubated for 24 hours. Fresh cell culture medium and 10% dimethyl sulfoxide (DMSO, Invitrogen, US) were used as negative and positive controls, respectively. On day 2, the extracts were replaced with a mixed solution of 100 μL / well of MTS reagent and cell culture medium (1:5 dilution), and the plate was incubated for approximately 3 hours.

[0303] The absorbance of the formazan product was measured at 490 nm using a microplate reader (PerkinElmer, US), and the cell viability was calculated based on the formula established in ISO 10993-5 (2009-06-01): where OD e is the average value of the optical density of the test sample extract measured, and OD nc is the average value of the optical density of the negative control group measured. The average value of the optical density of the cell culture medium background measured was subtracted from the OD e and OD nc values. Each alloy was measured in triplicate in the MTS assay. The MTS assay was independently repeated three times. The cell viability data were analyzed by using one-way analysis of variance (ANOVA), followed by Tukey's post hoc test. Two data sets with a significance level of p < 0.05 were considered to have a statistical difference.

[0304] Figure 22 Figure shows the cell viability of MG-63 osteoblasts exposed to extracts of M5, M6, and M7 alloys at 8 different concentrations and the Mg-0.4Zn-0.1Ca alloy of Example 11 as a reference material for 24 hours. According to ISO 10993-5 (2009-06-01), the dashed line across the middle of each tile indicates the threshold (70% cell viability) between the toxic reaction and the non-toxic reaction. Obviously, in general, when the extracts of the dilute zinc alloys are diluted to 50% or lower, a non-toxic reaction occurs, which is similar to the reference material (Mg-0.4Zn-0.1Ca).

[0305] Example 9: Effect of extrusion temperature

[0306] Uniaxial compression was performed on M3 and M4 alloy samples extruded at two different temperatures, and the true stress-strain curves are shown in Figure 23 and 24 . The values of the compressive yield strength of the extruded M3 and M4 alloy samples are listed in Table 12. When the extrusion temperature increased from 250 °C to 350 °C, the compressive yield strength of both M3 and M4 alloys increased.

[0307]

[0308] Example 10 (comparative): Effect of extrusion temperature on the annealing strengthening response of M3 and M4 alloys

[0309] The effect of extrusion temperature on the annealing strengthening response was investigated in M3 and M4 alloys. The same pre-extrusion homogenization conditions as in Examples 1 and 2 were used. The M3 alloy was extruded and homogenized at 175 °C, and the M4 alloy was extruded and homogenized at 165 °C. The extrusion ratio was controlled at 36:1, and the pusher speed was controlled at 0.1 mm·s -1 . The extrusion and annealing conditions are listed in Table 13.

[0310]

[0311]

[0312] After hot extruding the M3 alloy at 175 °C and the M4 alloy at 165 °C, post-extrusion annealing treatments were carried out at 250 °C, 300 °C, and 350 °C for 2 hours. Both the 175 °C extruded M3 alloy and the 165 °C extruded M4 alloy that underwent post-extrusion annealing at 300 °C exhibited non-basal textures, as shown in Figure 25 (where (a) is the extruded M3 alloy and (b) is the subsequently annealed M3 alloy) and Figure 26 (where (a) is the extruded M4 alloy and (b) is the subsequently annealed M4 alloy).

[0313] Uniaxial compression was performed on the extruded samples and the samples annealed under three different conditions, and the true stress-strain curves of the M3 and M4 alloys are shown in Figure 27 and 28 respectively. The compressive yield strength values of the extruded and annealed M3 and M4 alloy samples are listed in Table 14. It was found that when the extrusion temperature for the M3 alloy was reduced to 175 °C and the extrusion temperature for the M4 alloy was reduced to 165 °C, the annealing strengthening behavior was eliminated. For the M3 and M4 alloys extruded at 175 °C and 165 °C respectively, the extruded samples and the samples that underwent post-extrusion annealing at 300 °C for 2 hours were evaluated under uniaxial tensile tests at room temperature and a strain rate of 10 -3 s -1 , and their tensile yield strength values are listed in Table 14. There was no annealing strengthening reaction during tensile deformation.

[0314]

[0315] Example 11 (comparative): Creep test of Mg-0.4Zn-0.1Ca alloy

[0316] The creep curves of a dilute magnesium alloy with the formula Mg-0.4Zn-0.1Ca (nominally containing 0.4 wt.% Zn and 0.1 wt.% Ca), extruded at 220 °C or 400 °C and examined at 37 °C (body temperature) under a load stress of 250 MPa, are shown in Figure 29Shown in. Compared with the Mg-0.4Zn-0.1Ca alloy under the same creep conditions, the creep resistance of the currently disclosed dilute zinc alloy is excellent.

[0317] Example 12 (comparison): Pure zinc

[0318] At a temperature above 150 °C, pure zinc was extruded into a cylindrical rod with a diameter of 6 mm at a punch speed of 0.1 mm·s -1 The extrusion ratio was controlled to be approximately 36:1. After hot extrusion, an annealing treatment was carried out at a temperature of 200 °C for 0.5 hours.

[0319] Figure 30 Shows the microstructure (left image) and grain size distribution (right image) of pure zinc, which are (a) 150E and (b) 150E + 200 °C / 0.5 h, respectively. Figure 31 Shows the texture of two identical samples.

[0320] At room temperature and a strain rate of 10 -3 s -1 Uniaxial compressive deformation was carried out on the extruded and annealed samples along the extrusion direction. The true stress-strain curve is shown in Figure 32 The compressive yield strength of the extruded alloy (150E) was only 74 MPa, and the compressive yield strength of the annealed sample (150E + 200 °C / 0.5 h) was only 132 MPa. The strength of the extruded sample of pure zinc was insufficient to fabricate or process samples for tensile testing.

Claims

1. A method for preparing a dilute zinc alloy, the method comprising the following steps: (a) Extruding and homogenizing the dilute zinc alloy at a temperature above 175 °C; and (b) Optionally annealing the extruded dilute zinc alloy at a temperature of about 250 °C to about 400 °C; wherein the dilute zinc alloy contains at least 99.0 wt.% zinc; and one or both of iron and copper in a total amount of about 0.01 wt.% to about 0.99 wt.%; wherein the dilute zinc alloy contains one or more of magnesium, calcium, manganese, and lithium in an amount of about 0.01 wt.% to about 0.7 wt.%; and wherein the sum of iron, copper, and one or more of magnesium, calcium, manganese, and lithium does not exceed about 1.0 wt.%.

2. The method according to claim 1, wherein the dilute zinc alloy contains at least 99.0 wt.% zinc; and one or both of iron and copper in a total amount of about 0.03 wt.% to about 0.78 wt.%; wherein the dilute zinc alloy contains one or more of magnesium, calcium, manganese, and lithium in an amount of about 0.02 wt.% to about 0.7 wt.%; and wherein the sum of iron, copper, and one or more of magnesium, calcium, manganese, and lithium does not exceed 0.8 wt.%.

3. The method according to claim 1, wherein the dilute zinc alloy contains at least 99.0 wt.% zinc; and, about 0.02 wt.% to about 0.97 wt.% iron and about 0.01 wt.% to about 0.1 wt.% copper, or about 0.06 wt.% to about 0.5 wt.% copper and about 0.01 wt.% to about 0.19 wt.% iron; wherein the dilute zinc alloy contains one or more of magnesium, calcium, manganese, and lithium in an amount of about 0.01 wt.% to about 0.2 wt.%; and wherein the sum of iron, copper, and one or more of magnesium, calcium, manganese, and lithium does not exceed 1.0 wt.%.

4. The method according to claim 1, wherein the dilute zinc alloy contains at least 99.5 wt.% zinc; and, about 0.02 wt.% to about 0.5 wt.% iron and about 0.01 wt.% to about 0.06 wt.% copper, or about 0.06 wt.% to about 0.2 wt.% copper and about 0.01 wt.% to about 0.05 wt.% iron; wherein the dilute zinc alloy contains one or more of magnesium, calcium, manganese, and lithium in an amount of about 0.01 wt.% to about 0.2 wt.%; and wherein the sum of iron, copper, and one or more of magnesium, calcium, manganese, and lithium does not exceed 0.5 wt.%.

5. The method according to claim 1 or claim 2, wherein the sum of iron, copper, and one or more of magnesium, calcium, manganese, and lithium does not exceed 0.7 wt.%, or 0.6 wt.%, or 0.5 wt.%, or 0.4 wt.%, or 0.3 wt.%.

6. The method according to any one of claims 1 to 5, wherein the dilute zinc alloy has a strong basal texture after extrusion.

7. The method according to any one of claims 1 to 6, wherein the dilute zinc alloy has a strong basal texture after annealing.

8. The method according to any one of claims 1 to 7, wherein the extrusion is carried out at a temperature higher than 200 °C.

9. The method according to any one of claims 1 to 7, wherein the extrusion is carried out at a temperature of about 200 °C to about 380 °C.

10. The method according to any one of claims 1 to 9, wherein the extrusion speed is from about 0.01 mm . s -1 to about 10 mm . s -1 , or from about 0.05 mm . s -1 to about 0.5 mm . s -1 .

11. The method according to any one of claims 1 to 10, wherein the extrusion ratio is about 8:1 to about 80:1, or about 19:1 to about 50:

1.

12. The method according to any one of claims 1 to 11, wherein the annealing is carried out at a temperature of about 250 °C to about 350 °C.

13. The method according to any one of claims 1 to 12, wherein the annealing is carried out for about 0.5 hour to about 50 hours, or about 1 hour to about 10 hours.

14. The method according to any one of claims 1 to 13, which comprises a homogenization step before extrusion, wherein the dilute zinc alloy is maintained at a temperature of about 300 °C to about 400 °C for a period of up to about 5 hours.

15. The method according to any one of claims 1 to 14, wherein the average grain size of the dilute zinc alloy after extrusion is greater than 5 microns or greater than 10 microns.

16. The method according to any one of claims 1 to 15, wherein the average grain size of the dilute zinc alloy after extrusion is less than 25 microns.

17. The method according to any one of claims 1 to 16, wherein the annealing process increases the average grain size of the dilute zinc alloy.

18. The method according to any one of claims 1 to 17, wherein the average grain size of the dilute zinc alloy after annealing is greater than 25 microns.

19. The method according to any one of claims 1 to 17, wherein the average grain size of the dilute zinc alloy after annealing is about 25 microns to about 1000 microns.

20. The method according to any one of claims 1 to 19, wherein the annealing process increases the ambient temperature compressive yield strength of the dilute zinc alloy.

21. The method according to any one of claims 1 to 20, wherein the annealing process reduces the minimum creep rate of the dilute zinc alloy.

22. The method according to any one of claims 1, 2 or 5 to 21, wherein the dilute zinc alloy comprises: (a) at least 99.0 wt.% zinc; (b) about 0.01 wt.% iron; (c) about 0.04 wt.% copper; and (d) about 0.05 wt.% magnesium; or (a) at least 99.0 wt.% zinc; (b) about 0.06 wt.% copper; and (c) about 0.04 wt.% magnesium; or (a) at least 99.0 wt.% zinc; (b) about 0.06 wt.% iron; (c) about 0.14 wt.% copper; (d) about 0.01 wt.% calcium; (e) about 0.09 wt.% manganese; and (f) about 0.16 wt.% magnesium; or (a) at least 99.0 wt.% zinc; (b) about 0.01 wt.% iron; (c) about 0.37 wt.% copper; (d) about 0.05 wt.% manganese; and (e) about 0.18 wt.% magnesium; or (a) at least 99.0 wt.% zinc; (b) about 0.02 wt.% iron; (c) about 0.1 wt.% copper; (d) about 0.02 wt.% calcium; (e) about 0.16 wt.% manganese; and (f) about 0.15 wt.% magnesium.

23. A dilute zinc alloy formed by the method according to any one of claims 1 to 22.

24. A dilute zinc alloy comprising: at least 99.0 wt.% zinc; and one or both of iron and copper in a total amount of about 0.01 wt.% to about 0.99 wt.%; wherein the dilute zinc alloy comprises one or more of magnesium, calcium, manganese, and lithium in an amount of about 0.01 wt.% to about 0.7 wt.%; and wherein the sum of iron, copper, and one or more of magnesium, calcium, manganese, and lithium does not exceed about 1.0 wt.%.

25. The dilute zinc alloy according to claim 24, wherein the dilute zinc alloy comprises: at least 99.0 wt.% zinc; and one or both of iron and copper in a total amount of about 0.03 wt.% to about 0.78 wt.%; wherein the dilute zinc alloy comprises one or more of magnesium, calcium, manganese, and lithium in an amount of about 0.02 wt.% to about 0.7 wt.%; and wherein the sum of iron, copper, and one or more of magnesium, calcium, manganese, and lithium does not exceed 0.8 wt.%.

26. The dilute zinc alloy according to claim 24, which comprises: (a) at least 99.0 wt.% zinc; (b) about 0.02 wt.% to about 0.97 wt.% iron and about 0.01 wt.% to about 0.1 wt.% copper, or about 0.06 wt.% to about 0.5 wt.% copper and about 0.01 wt.% to about 0.19 wt.% iron; (c) one or more of magnesium, calcium, manganese, and lithium in an amount of about 0.01 wt.% to about 0.12 wt.%; wherein the sum of iron, copper, and one or more of magnesium, calcium, manganese, and lithium does not exceed 1.0 wt.%.

27. The dilute zinc alloy according to claim 24, wherein the dilute zinc alloy comprises: (a) at least 99.5 wt.% zinc; (b) about 0.02 wt.% to about 0.5 wt.% iron and about 0.01 wt.% to about 0.06 wt.% copper, or about 0.06 wt.% to about 0.2 wt.% copper and about 0.01 wt.% to about 0.05 wt.% iron; (c) one or more of magnesium, calcium, manganese, and lithium in an amount of about 0.01 wt.% to about 0.12 wt.%; wherein the sum of iron, copper, and one or more of magnesium, calcium, manganese, and lithium does not exceed 0.5 wt.%.

28. The dilute zinc alloy according to claim 24 or 25, wherein the sum of iron, copper, and one or more of magnesium, calcium, manganese, and lithium does not exceed 0.7 wt.%, or 0.6 wt.%, or 0.5 wt.%, or 0.4 wt.%, or 0.3 wt.%.

29. The dilute zinc alloy according to any one of claims 24 to 28, wherein the dilute zinc alloy has a strong basal texture.

30. The dilute zinc alloy according to any one of claims 24 to 29, wherein the average grain size of the dilute zinc alloy is greater than 5 microns, or greater than 10 microns, or greater than 25 microns.

31. The dilute zinc alloy according to any one of claims 24 to 29, wherein the average particle size of the dilute zinc alloy is from about 5 microns to about 1000 microns.

32. The dilute zinc alloy according to any one of claims 24 to 31, wherein when measured at an ambient temperature and a strain rate of 10 -3 s -1 , the compressive strength of the dilute zinc alloy is greater than 220 MPa, or greater than 230 MPa, or greater than 240 MPa, or greater than 250 MPa, or greater than 260 MPa, or greater than 270 MPa, or greater than 280 MPa, or greater than 290 MPa, or greater than 300 MPa.

33. The dilute zinc alloy according to any one of claims 24 to 32, wherein the minimum compressive creep rate of the dilute zinc alloy is less than 3×10 -6 s -1 at 37 °C under a load stress of 200 MPa, or less than 2×10 -6 s -1 , or less than 1×10 -6 s -1 , or less than 5×10 -7 s -1 , or less than 3×10 -7 s -1 , or less than 2×10 -7 s -1 , or less than 1×10 -7 s -1 .

34. The dilute zinc alloy according to any one of claims 24, 25 or 28 to 33, wherein the dilute zinc alloy comprises: (a) at least 99.0 wt.% zinc; (b) about 0.01 wt.% iron; (c) about 0.04 wt.% copper; and (d) about 0.05 wt.% magnesium; or (a) at least 99.0 wt.% zinc; (b) about 0.06 wt.% copper; and (c) about 0.04 wt.% magnesium; or (a) at least 99.0 wt.% zinc; (b) about 0.06 wt.% iron; (c) about 0.14 wt.% copper; (d) about 0.01 wt.% calcium; (e) about 0.09 wt.% manganese; and (f) about 0.16 wt.% magnesium; or (a) at least 99.0 wt.% zinc; (b) about 0.01 wt.% iron; (c) about 0.37 wt.% copper; (d) about 0.05 wt.% manganese; and (e) about 0.18 wt.% magnesium; or (a) at least 99.0 wt.% zinc; (b) about 0.02 wt.% iron; (c) about 0.1 wt.% copper; (d) about 0.02 wt.% calcium; (e) about 0.16 wt.% manganese; and (f) about 0.15 wt.% magnesium.

35. An article comprising the dilute zinc alloy according to any one of claims 24 to 34.

36. The article according to claim 35, wherein the article is a medical implant.

37. The article according to claim 36, wherein the medical implant is a stent, plate, screw, nail, steel needle or support frame.

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