A low-chromium-content medium-strength high-conductivity Cu-Cr-Sn-Zn alloy and a preparation method thereof

Abstract

The application adopts a machine learning method to design a low-chromium-content medium-strength high-conductivity Cu-Cr-Sn-Zn alloy and a preparation process thereof, and belongs to the technical field of new material design and processing. The developed low-chromium-content Cu-Cr-Sn-Zn alloy has the following component characteristics: the content of Cr is 0.10wt%-0.50wt%, the content of Sn is 0.05wt%-0.50wt%, the content of Zn is 0.10wt%-0.50wt%, the content of La is 0.001wt%-0.10wt%, and the balance is Cu. According to the needs, one or more micro-alloying elements such as Mg, Zr, P or Ce can also be added to improve the comprehensive performance of the alloy. The content of the micro-alloying element is 0.00wt%-0.30wt% Mg, 0.00wt%-0.20wt% Zr, 0.00wt%-0.10wt% P and 0.00wt%-0.10wt% Ce. The application cooperatively optimizes the content of Cr, Sn and Zn in the alloy, and thus significantly improves the comprehensive mechanical and electrical performance of the copper alloy. The tensile strength can reach 600-650 MPa, and the conductivity can reach 75%IACS-80%IACS, which is suitable for large-scale industrial production and application.

Description

TECHNICAL FIELD

[0001] The present application relates to a new type of medium-strength high-conductivity copper alloy and its preparation process, belonging to the technical field of metal material design, preparation and processing, and particularly provides a composition and preparation process of a low-chromium-content, low-cost Cu-Cr-Sn-Zn alloy. BACKGROUND

[0002] Copper alloys have been widely used in the fields of electricity, communication, machinery, etc. due to their high strength, high conductivity, good elasticity, small elastic hysteresis and fatigue resistance. Among them, high-strength high-conductivity copper alloys are widely used in integrated circuit lead frame, electrified railway contact wire, etc. due to their outstanding comprehensive performance of strength and conductivity. In particular, with the development of integrated circuits towards high density, miniaturization, multifunction and low cost, copper alloy lead frame materials matching the packaging process are developing towards multi-pin, high density, ultra-thin and miniaturization, and therefore higher requirements are put forward for the comprehensive performance such as conductivity and strength of lead frame copper alloys.

[0003] Currently widely used copper alloys for lead frames mainly include Cu-Fe-P alloy, Cu-Ni-Si alloy, etc. It is difficult to meet the demand of high strength, excellent conductivity and heat conduction performance, good forming performance and low cost, and large-scale commercial application. The ideal lead frame material is a material with high strength, high conductivity, excellent processing performance, tensile strength of more than 600 MPa, electrical conductivity of more than 75%, and softening resistance temperature of more than 500℃.

[0004] Cu-Cr-Sn-Zn alloy has excellent stamping formability, electroplating property, joining property, brazing property and softening resistance, and has high strength and conductivity, which is the main research direction of medium-strength high-conductivity copper alloy for lead frame in the world. It is of great significance to develop an easy-to-etch Cu-Cr-Sn-Zn alloy with high strength and high conductivity comprehensive performance and its preparation process to meet the application requirements of large or super large scale integrated circuit lead frame materials. SUMMARY

[0005] The present application reduces the content of Cr element, precisely controls the contents of Cr, Sn and Zn elements, and further improves the strength and conductivity comprehensive performance of copper alloy. Machine learning method is used to analyze the composition-performance data of medium-strength high-conductivity copper alloy reported in public, the data is analyzed by feature engineering, a key alloy factor-performance model is established, the design results are verified by experiment and performance test, high-performance copper alloy efficient composition design is realized, and a composition and preparation process of a high-comprehensive-performance, low-chromium-content medium-strength high-conductivity Cu-Cr-Sn-Zn alloy is developed through alloy element content optimization and reasonable preparation process formulation.

[0006] A low-chromium-content medium-strength high-conductivity Cu-Cr-Sn-Zn alloy is characterized in that the content of Cr is 0.10wt%-0.50wt%, the content of Sn is 0.05wt%-0.50wt%, the content of Zn is 0.10wt%-0.50wt%, the content of La is 0.001wt%-0.10wt%, and the balance is Cu.

[0007] Further, one or more micro-alloying elements such as Mg, Zr, P or Ce can be added as needed to improve the overall performance of the alloy. The content of the micro-alloying elements is 0.00wt%-0.30wt% Mg, 0.00wt%-0.20wt% Zr, 0.00wt%-0.10wt% P, and 0.00wt%-0.10wt% Ce.

[0008] The preparation process of the low-chromium-content Cu-Cr-Sn-Zn alloy of the application is shown in Figure 1 which is characterized in that the preparation process flow is: smelting→homogenization treatment→hot rolling→rough cold rolling→solid solution quenching→first fine cold rolling→first aging→second fine cold rolling→second aging→third fine cold rolling; the specific process steps are as follows:

[0009] (1) Smelting: Put the proportioned electrolytic Cu raw material into the smelting furnace and heat it to 1200-1300℃; after complete melting, add electrolytic Sn, Cu-Zn, Cu-Cr, Cu-La, Cu-Mg, Cu-Zr, Cu-P, and Cu-Ce intermediate alloys into the metal liquid, cover the metal surface with roasted charcoal / bamboo charcoal to prevent oxidation; after the smelted alloy melt is left to stand for 10-30 minutes, remove the slag, and keep the temperature at 1200±10℃; then cast into a flat ingot, remove surface defects after cooling to room temperature;

[0010] (2) Homogenization treatment: homogenize the flat ingot after removing surface defects at 800-1000℃ for 1-8h;

[0011] (3) Hot rolling: hot roll the homogenized blank, with an opening rolling temperature of 800℃, a final rolling temperature ≥700℃, a hot rolling pass reduction of 30%-50%, and a total deformation of 60%-95%;

[0012] (4) Rough cold rolling: pass deformation of 20%-40% and total deformation of 50%-90%;

[0013] (5) Solid solution quenching: online inert gas protection solid solution quenching;

[0014] (6) First fine cold rolling: pass deformation of 10%-30% and total deformation of 30%-80%;

[0015] (7) First aging: cover-type furnace aging with inert gas protection;

[0016] (8) Secondary cold rolling: pass deformation 10%~30%, total deformation 20%~70%;

[0017] (9) Secondary aging: cover furnace aging, inert gas protection;

[0018] (10) Third cold rolling: pass deformation 10%~30%, total deformation 20%~70%.

[0019] Further, the solid solution temperature in step (5) is 900~1000℃.

[0020] Further, the primary aging temperature in step (7) is 400~550℃, and the holding time is 1~5h.

[0021] Further, the secondary aging temperature in step (9) is 350~500℃, and the holding time is 2~8h.

[0022] Technical points of the present application:

[0023] The present application analyzes the composition-performance data of the medium-strength high-conductivity copper alloy reported in the public report by using the machine learning method, optimizes the content of elements such as Cr, Sn and Zn in the alloy, and obtains a low-chromium-content medium-strength high-conductivity Cu-Cr-Sn-Zn alloy with excellent comprehensive performance. In the alloy composition design process, under the premise of ensuring the strength and conductivity of the alloy, the present application maximally reduces the content of Cr element and ensures that the total content of alloy elements is as low as possible to reduce the cost of the alloy; multiple deformation-heat treatment can maximally promote the precipitation of Cr precipitates in the alloy to realize the comprehensive performance of high strength and high conductivity.

[0024] An invention patent with the authorization number CN107299246B and the patent name of a high-strength high-conductivity CuCrMgSn-Ce alloy wire and its preparation method is published on the website of the patent office. The composition includes Cu, Cr, Mg, Sn, Ce elements and unavoidable impurities, wherein Cu is the alloy matrix, and the mass ratio is higher than 98%, the mass ratio of other components is as follows: Cr 0.10~0.40%, Mg 0.02~0.15%, Sn 0.02~0.10%, Ce 0.02~0.10%, and the total mass ratio of Mg and Sn is between 0.08~0.17%, and the total mass of unavoidable impurities is less than 0.05%.

[0025] Compared with the comparative file CN107299246B, the innovation point of the present application is that the combination of Sn and Zn can promote the precipitation of Cr element, refine the Cr precipitates to 20~100nm, and effectively improve the etching performance of the alloy after being prepared into a frame.

[0026] Advantages of the present application:

[0027] (1) The present application comprehensively considers the comprehensive influence of each element on the microstructure and properties of the medium-strength high-conductivity Cu-Cr-Sn-Zn alloy when designing the composition, especially the careful selection and optimization of Cr, Sn, Zn, La and other elements, which plays a significant role in reducing the alloy cost and improving the alloy performance. The specific considerations are as follows:

[0028] The Cr element is mainly a constituent element of the precipitated phase Cr phase.

[0029] The Sn element is mainly added to promote the precipitation of the precipitated phase, inhibit the coarsening of the precipitated phase, and improve the mechanical and electrical properties of the alloy.

[0030] The Zn element is added to strengthen the alloy matrix on the one hand, and to promote the precipitation of the precipitated phase on the other hand, thereby improving the mechanical and electrical properties of the alloy.

[0031] The La element has the following effects: ① It is easy to react with oxygen, sulfur, hydrogen and some impurities during smelting, has the effects of desulfurization, dehydrogenation and impurity removal, can improve the alloy structure, make the alloy structure more pure, and effectively improve the electrical conductivity of the alloy; ② It can significantly reduce the interfacial energy at the grain boundary, thereby reducing the driving force of interfacial movement and improving the mechanical properties of the alloy; ③ It can promote the precipitation of the precipitated phase and improve the electrical properties of the alloy.

[0032] (2) The smelting process of the present application can avoid the problems of insufficient melting of high-melting-point elements and burning loss of trace elements and easily oxidized elements, thereby improving the accuracy and uniformity of the chemical composition of the ingot.

[0033] (3) The deformation-heat treatment process of the present application can improve the precipitation degree of the precipitated phase in the alloy, improve the comprehensive mechanical and electrical properties of the alloy, and the prepared alloy has a lower comprehensive cost, and the performance can reach 600-650 MPa, 75% IACS-80% IACS. BRIEF DESCRIPTION OF DRAWINGS

[0034] Figure 1 The figure is a preparation process flow chart of the low-chromium-content Cu-Cr-Sn-Zn alloy. DETAILED DESCRIPTION

[0035] The technical solutions of the present application will be further described below in combination with the drawings and examples.

[0036] Example: The present application develops a low-chromium-content medium-strength high-conductivity Cu-Cr-Sn-Zn alloy for the purpose of reducing the content of Cr element, accurately controlling the contents of Cr, Sn, Zn and other elements, and thereby improving the strength and comprehensive conductivity of the copper alloy. The composition is shown in Table 1.

[0037] Table 1 Composition of low chromium content medium strength high conductivity Cu-Cr-Sn-Zn alloy (wt%)

[0038]

[0039] The preparation process of the alloy is as follows:

[0040] (1) Melting: Put the proportioned electrolytic Cu raw material (purity greater than 99.99%) into a melting furnace and heat to 1200-1300°C; after complete melting, add electrolytic Sn, Cu-Zn, Cu-Cr, Cu-La, Cu-Mg, Cu-Zr, Cu-P, Cu-Ce intermediate alloy into the metal liquid, cover the metal surface with roasted charcoal / bamboo charcoal to prevent oxidation; after the melted alloy is placed for 20 minutes, remove the slag, and the temperature is kept at 1200±10°C; then cast into a flat ingot, remove surface defects after cooling to room temperature;

[0041] (2) Homogenization treatment: place the flat ingot after removing surface defects at 800°C for 2h;

[0042] (3) Hot rolling: hot rolling deformation is performed on the homogenized material, the opening rolling temperature is 800°C, the final rolling temperature is ≥700°C, the pass reduction of hot rolling is 30%-50%, and the total deformation is 80%;

[0043] (4) Rough cold rolling: the pass deformation is 20%-40%, the total deformation is 70%, and the thickness after rolling is 10mm;

[0044] (5) Solid solution quenching: online inert gas protection solid solution quenching, solid solution temperature is 1000°C;

[0045] (6) First fine cold rolling: the pass deformation is 10%-30%, the total deformation is 70%, and the thickness after rolling is 2.0mm;

[0046] (7) First aging: cover type furnace aging, inert gas protection, temperature is 500°C, and the holding time is 1h;

[0047] (8) Second fine cold rolling: the pass deformation is 10%-30%, the total deformation is 67%, and the thickness after rolling is 1.0mm;

[0048] (9) Second aging: cover type furnace aging, inert gas protection, temperature is 450°C, and the holding time is 5h;

[0049] (10) Third fine cold rolling: the pass deformation is 10%-30%, the total deformation is 50%, and the thickness after rolling is 0.5mm.

[0050] The high temperature softening resistance temperature of the prepared alloy is all above 500°C, and the strength and conductivity performance is shown in Table 2.

[0051] Table 2 Properties of low chromium content medium strength high conductivity Cu-Cr-Sn-Zn alloys

[0052]

Claims

1. A preparation process for a low-chromium-content, medium-strength, high-conductivity Cu-Cr-Sn-Zn alloy, characterized in that: The preparation process is as follows: smelting → homogenization treatment → hot rolling → rough cold rolling → solution quenching → first precision cold rolling → first aging → second precision cold rolling → second aging → third precision cold rolling. The specific steps are as follows: (1) Smelting: The electrolytic Cu raw material prepared in proportion is placed in the smelting furnace and heated to 1200℃~1300℃; after it is completely melted, the electrolytic Sn, Cu-Zn, Cu-Cr, Cu-La, Cu-Mg, Cu-Zr, Cu-P, and Cu-Ce intermediate alloys are added to the molten metal. The surface of the metal is covered with baked charcoal / bamboo charcoal to prevent oxidation; the smelted alloy melt is allowed to stand for 10~30 minutes and then the slag is removed, and the temperature is maintained at 1200±10℃; then it is cast into flat ingots, cooled to room temperature, and surface defects are removed. (2) Homogenization treatment: After removing surface defects, the flat ingot is kept at 800-1000℃ for 1-8 hours; (3) Hot rolling: The homogenized billet is hot rolled and deformed. The initial rolling temperature is 800℃, the final rolling temperature is ≥700℃, the reduction per hot rolling pass is 30%~50%, and the total deformation is 60%~95%. (4) Rough cold rolling: 20% to 40% deformation per pass, 50% to 90% total deformation; (5) Solution quenching: Online solution quenching under inert gas protection; (6) One-pass precision cold rolling: 10% to 30% deformation per pass, 30% to 80% total deformation; (7) Single aging: bell-type furnace aging, inert gas protection; (8) Secondary precision cold rolling: 10% to 30% deformation per pass, 20% to 70% total deformation; (9) Secondary aging: bell-type furnace aging, inert gas protection; (10) Three-stage precision cold rolling: 10% to 30% deformation per pass, 20% to 70% total deformation; The microalloying elements consist of 0.00wt%–0.30wt% Mg, 0.00wt%–0.20wt% Zr, 0.00wt%–0.10wt% P, 0.00wt%–0.10wt% Ce, 0.10wt%–0.50wt% Cr, 0.05wt%–0.50wt% Sn, 0.10wt%–0.50wt% Zn, 0.001wt%–0.10wt% La, with the balance being Cu.

2. The preparation process of the low-chromium-content, medium-strength, high-conductivity Cu-Cr-Sn-Zn alloy as described in claim 1, characterized in that... The solution temperature in step (5) is 900–1000 °C.

3. The preparation process of the low-chromium-content, medium-strength, high-conductivity Cu-Cr-Sn-Zn alloy as described in claim 1, characterized in that... The aging temperature in step (7) is 400-550℃, and the holding time is 1-5 hours.

4. The preparation process of the low-chromium-content, medium-strength, high-conductivity Cu-Cr-Sn-Zn alloy as described in claim 1, characterized in that... The secondary aging temperature in step (9) is 350-500℃, and the holding time is 2-8 hours.

Images