Aluminum alloys for casting and aluminum alloy castings

Abstract

The present invention provides an aluminum alloy for casting, the aluminum alloy enabling the achievement of an Al-Si based alloy casting in which Al-(Fe, Mn, Cr)-Si crystallized products are miniaturized without being restricted by the casting method even if the Fe content is increased. The present invention also provides an aluminum alloy casting which has excellent proof stress, excellent ductility and excellent toughness at the same time even if the Fe content is increased, by reducing the influence of Fe that is contained therein as an impurity. An aluminum alloy for casting according to the present invention is characterized by containing more than 3.0% by mass but not more than 12.0% by mass of Si, 0.2% to 0.8% by mass of Fe, 0.1% to 0.7% by mass of Mn, 0.05% to 0.4% by mass of Cr and 0.05% to 0.3% by mass of V.

Description

[Technical Field]

[0001] The present invention relates to a eutectic Al-Si alloy for casting having excellent toughness and a casting material thereof. [Background technology]

[0002] Al-Si alloys have been used as casting alloys because they have good castability and the resulting casting materials exhibit excellent mechanical properties. However, there is a strong demand for lower prices for casting alloys, and the proportion of scrap material in the raw materials is higher than that of wrought alloys. In addition, from the perspectives of resource conservation and environmental protection, aluminum alloy castings are increasingly being produced from recycled ingots.

[0003] However, Al-Si alloy castings made from recycled ingots are prone to contain Fe as an impurity. Fe has the effect of preventing seizure on the mold during casting and improving tensile strength, but as the Fe content increases, coarse Al-Fe-Si crystals, which can become the starting point for fracture when stress is applied, are more likely to form.

[0004] To cope with this, Mn and Cr are added to form Al-(Fe, Mn, Cr)-Si crystallized products, which are less likely to coarsen, instead of Al-Fe-Si crystallized products.

[0005] For example, Patent Document 1 (JP 2006-322062 A) discloses a casting aluminum alloy containing 2.0 to 6.0 weight percent Si, 0.1 to 1.5 weight percent Mg, 0.1 to 1.3 weight percent Cr, and the balance consisting of Al and unavoidable impurities, with up to 0.8 weight percent Fe being permitted among the unavoidable impurities.

[0006] In the casting aluminum alloy described in Patent Document 1, the Si content is set in the range of 2.0 to 6.0 wt % to suppress a decrease in elongation of the aluminum alloy, the Cr content is added in the range of 0.1 to 1.3 wt % to suppress a decrease in elongation of the alloy while preventing seizure between the aluminum alloy and the mold during casting even when the casting temperature is high, and the Mg content is added in the range of 0.1 to 1.5 wt % to suppress a decrease in elongation while improving the yield strength of the aluminum alloy.

[0007] Furthermore, Patent Document 2 (JP 2020-158788 A) discloses an aluminum alloy consisting of, based on the total mass being 100%, 7-10% Si, 0.3-0.9% Fe, 0.05-0.3% V, 0.05-0.3% Zr, 0.05-0.3% Ti, and the remainder being Al and impurities.

[0008] In the aluminum alloy described in Patent Document 2, the coexistence (composite addition) of Zr and Ti makes it possible to crystallize fine Fe-based compounds in a substantially uniformly dispersed manner around the Al matrix, and it is said that die-cast products made from this aluminum alloy exhibit high strength and high ductility without the need for heat treatment. [Prior art documents] [Patent documents]

[0009] [Patent Document 1] Japanese Patent Application Laid-Open No. 2006-322062 [Patent Document 2] Japanese Patent Publication No. 2020-158788 Summary of the Invention [Problem to be solved by the invention]

[0010] In the aluminum alloy for casting described in Patent Document 1, the addition of 0.1 to 1.3 wt % of Cr converts the Fe-based compounds into an Al-Si-Cr-Fe phase, and by configuring the Fe-based compounds in this manner, it is said that it is possible to reduce the decrease in elongation and prevent the occurrence of seizure during casting. However, simply converting the Fe-based compounds into an Al-Si-Cr-Fe phase does not sufficiently ensure elongation and toughness. This problem becomes more pronounced in particular when the die-cast material is not one in which the structure containing the Al-Si-Cr-Fe phase is easily refined.

[0011] In the aluminum alloy described in Patent Document 2, most of the V and Zr are expelled to the outer periphery of the α-Al and concentrated there, resulting in fine dispersion of Fe-based compounds in the outer periphery of the α-Al. However, this mechanism means that the segregation of brittle Fe-based compounds to the grain boundaries of the α-Al is promoted, and the network structure of the brittle phase reduces the toughness of the aluminum alloy casting.

[0012] If the grain boundary area can be increased by refining α-Al and the amount of Fe-based compounds formed can be sufficiently reduced, the mechanical properties of the aluminum alloy casting can be ensured, but the applicable casting conditions are significantly limited. Moreover, the examples shown in Patent Document 2 above are only for die-cast materials, and it is difficult to impart high strength, yield strength, and ductility to aluminum alloy castings obtained by general casting methods such as sand casting and metal mold casting.

[0013] In view of the above-mentioned problems in the prior art, an object of the present invention is to provide an aluminum alloy for casting, which can produce fine Al-(Fe, Mn, Cr)-Si crystals in the resulting Al-Si alloy casting, regardless of the casting method, even if the Fe content is increased. Another object of the present invention is to provide an aluminum alloy casting that has excellent yield strength, ductility, and toughness, even if the Fe content is increased, by reducing the influence of Fe contained as an impurity.

[0014] Another object of the present invention is to provide aluminum and aluminum alloy castings for casting that are suitable for horizontal recycling, etc., by reducing the adverse effects of Fe, which is likely to be mixed in from scrap. [Means for solving the problem]

[0015] In order to achieve the above object, the present inventors have conducted extensive research into the composition of Fe-containing aluminum alloys for casting, and as a result have found that adding Mn, Cr, and V in combination to a hypoeutectic Al-Si alloy is extremely effective, thereby arriving at the present invention.

[0016] That is, the present invention provides: Si: more than 3.0 mass% and 12.0 mass% or less, Fe: 0.2~0.8% by mass, Mn: 0.1~0.7% by mass, Cr:0.05~0.4% by mass, V: 0.05 to 0.3 mass%; The present invention provides an aluminum alloy for casting, characterized by:

[0017] Although Fe contributes to preventing seizure on the mold during casting and improving the tensile strength of aluminum alloy castings, an increase in the Fe content makes it easier for coarse Al-Fe-Si crystals to form, which can become the starting point for fracture when stress is applied. In contrast, the aluminum alloy for casting of the present invention is added with Mn and Cr to form Al-(Fe, Mn, Cr)-Si crystals, which are less likely to coarsen, rather than Al-Fe-Si crystals.

[0018] The greatest feature of the aluminum alloy for casting of the present invention is that the addition of V results in the formation of fine VSi2-based compounds. These VSi2-based compounds act as solidification nuclei to form fine CrSi2, which then undergo a peritectic reaction to form Al. 13 Si4Cr4 is formed and finally the Al 13Si4Cr4 acts as a solidification nucleus to form fine Al-(Fe, Mn, Cr)-Si crystals. That is, the formation of fine VSi2 compounds acts as a trigger to achieve significant refinement of the Al-(Fe, Mn, Cr)-Si crystals.

[0019] Although Fe forms brittle compounds and fundamentally reduces the toughness of aluminum alloys, 0.2 to 0.8 mass% Fe can reliably neutralize the adverse effects of Fe on the mechanical properties of Al-Si alloy castings by significantly refining Al-(Fe, Mn, Cr)-Si crystals with VSi2 compounds. As a result, recycled Al-Si alloy ingots containing Fe as an impurity can be used as a raw material.

[0020] Furthermore, the aluminum alloy for casting of the present invention preferably contains 0.2 to 2.0 mass% Cu, more than 0.2 mass% but not more than 1.0 mass% Mg, and one or more of 0.005 to 0.05 mass% Sr, 0.005 to 0.05 mass% Sb, and 0.005 to 0.25 mass% Ti, with the remainder consisting of Al and inevitable impurities.

[0021] The inclusion of 0.2 to 2.0 mass% Cu can increase the strength of aluminum alloy castings through solid solution strengthening and age hardening. Furthermore, Mg contributes to age hardening when coexisting with Si, and the inclusion of more than 0.2 mass% and not more than 1.0 mass% Mg can increase the strength of aluminum alloy castings.

[0022] Sr and Sb have the effect of refining eutectic Si, and this effect becomes significant at 0.005% by mass or more, but the effect does not improve even if added at 0.05% by mass or more. Ti has the effect of refining the cast structure (α phase), and this effect becomes significant at 0.005% by mass or more, but the effect does not improve even if added at 0.25% by mass or more.

[0023] The present invention also provides Si: 5.0~8.0% by mass, Fe:0.2~0.6% by mass, Mn: 0.1~0.3% by mass, Cr:0.1~0.3% by mass, V:0.05~0.2% by mass, Cu: 0.2~1.0% by mass, Mg: 0.2~0.6% by mass, Sr: 0.005~0.05% by mass, Ti: 0.005 to 0.25 mass%, The balance consists of Al and unavoidable impurities. Also provided is an aluminum alloy for casting, characterized by:

[0024] By strictly controlling the composition of the aluminum alloy for casting as described above, it is possible to more reliably achieve a significant refinement of Al-(Fe, Mn, Cr)-Si crystals, triggered by the formation of fine VSi2 compounds. Furthermore, it is possible to efficiently achieve the following: high strength of the aluminum alloy casting by adding Cu and Mg; refinement of eutectic Si by adding Sr; and refinement of the cast structure (α phase) by adding Ti. As a result, even if the Fe content is increased, it is possible to obtain an optimal aluminum alloy for casting, in which the Al-(Fe, Mn, Cr)-Si crystals in the resulting aluminum alloy casting are refined, regardless of the casting method.

[0025] Furthermore, the present invention also provides an aluminum alloy casting characterized by comprising the aluminum alloy for casting of the present invention.

[0026] The aluminum alloy casting of the present invention is made of the aluminum alloy for casting of the present invention, and since the influence of Fe contained as an impurity is reduced, it can exhibit excellent yield strength, ductility, and toughness even if the Fe content is increased. Here, the aluminum alloy casting of the present invention means one cast by various conventionally known casting methods (sand casting, metal mold casting, gravity casting, low-pressure casting, die casting, etc.), and is not limited to one cast by a specific casting method.

[0027] In the aluminum alloy casting of the present invention, it is preferable that the mode of length of the iron-based compounds is 12.5 μm or less. By refining the iron-based compounds such as Al-(Fe, Mn, Cr)-Si-based crystallized compounds and setting the mode of length to 12.5 μm or less, it is possible to impart excellent ductility and toughness to the aluminum alloy casting. It is also preferable that the iron-based compounds contain V. When the Al-(Fe, Mn, Cr)-Si-based crystallized compounds contain V, the refining effect resulting from the formation of VSi2-based compounds can be reliably achieved.

[0028] Furthermore, the aluminum alloy casting of the present invention preferably has a tensile elongation of 4% or more. When the aluminum alloy casting has a tensile elongation of 4% or more, it can be suitably used in applications where reliability is required. [Effects of the Invention]

[0029] According to the present invention, it is possible to provide an aluminum alloy for casting in which the Al-(Fe, Mn, Cr)-Si crystals in the resulting Al-Si alloy casting are refined, even when the Fe content is increased, without being limited by the casting method. Furthermore, by reducing the influence of Fe contained as an impurity, it is possible to provide an aluminum alloy casting that combines excellent proof stress, ductility, and toughness, even when the Fe content is increased. [Brief explanation of the drawings]

[0030] [Figure 1] 1 shows the microstructure of an example aluminum alloy casting 1. [Figure 2] 1 shows the microstructure of the example aluminum alloy casting 2. [Figure 3] 1 shows the microstructure of comparative aluminum alloy casting 1. [Figure 4] 1 shows the microstructure of comparative aluminum alloy casting 2. [Figure 5] 1 shows the microstructure of comparative aluminum alloy casting 3. [Figure 6] 1 shows the microstructure of comparative aluminum alloy casting 4. [Figure 7]1 is a histogram showing the length distribution of iron-based compounds in an example aluminum alloy casting 1. [Figure 8] 1 is an elemental mapping of an example aluminum alloy casting 1. DETAILED DESCRIPTION OF THE INVENTION

[0031] The aluminum alloy for casting and the aluminum alloy casting of the present invention will be described in detail below, but the present invention is not limited to these only.

[0032] 1. Aluminum alloys for casting The aluminum alloy for casting of the present invention is characterized by the combined addition of Mn, Cr and V to a hypoeutectic Al-Si alloy. Each component will be described in detail below.

[0033] (1) Essential additive elements Si: More than 3.0 mass% and 12.0 mass% or less Si has the effect of improving the castability of aluminum alloys and also the effect of improving mechanical properties such as tensile strength. This effect becomes significant when the content exceeds 3.0% by mass, but when added in an amount exceeding 12.0% by mass, eutectic Si and primary Si crystals tend to coarsen, resulting in a deterioration in mechanical properties. The amount of Si added is preferably 5.0 to 10.0% by mass, and more preferably 5.0 to 8.0% by mass.

[0034] Fe:0.2~0.8% by mass Fe has the effect of improving the mechanical properties of aluminum alloys, such as tensile strength, and of suppressing seizure on the mold during casting. These effects become significant at 0.2% by mass or more, but at more than 0.8% by mass, Al-(Fe, Mn, Cr)-Si crystals tend to become coarse.

[0035] Furthermore, when the casting aluminum alloy of the present invention is produced mainly from recycled ingots, it contains 0.2% by mass or more of Fe as an impurity. By setting the Fe content to 0.8% by mass or less, the adverse effects of Fe on the mechanical properties of aluminum alloy castings made from the casting aluminum alloy of the present invention can be reliably neutralized.

[0036] The Fe content is preferably 0.2 to 0.6% by mass. By setting the Fe content to 0.2 to 0.6% by mass, the adverse effects of Fe (deterioration of ductility and toughness) can be reliably suppressed while the effects of improving the strength and yield strength of the aluminum alloy casting and suppressing seizure to the mold are sufficiently exhibited.

[0037] Mn:0.1~0.7% by mass Mn crystallizes as fine Al-(Fe, Mn, Cr)-Si crystals and suppresses the formation of coarse Al-Fe-Si crystals. This effect is significant at 0.1% by mass or more, but if added in excess of 0.7% by mass, coarse Mn compounds are more likely to form. The Mn content is preferably 0.2 to 0.4% by mass, and more preferably 0.2 to 0.3% by mass.

[0038] Cr:0.1~0.4% by mass Cr crystallizes as fine Al-(Fe, Mn, Cr)-Si crystals and suppresses the formation of coarse Al-Fe-Si crystals. This effect is significant at 0.1% by mass or more, but if added in excess of 0.4% by mass, coarse Cr compounds are more likely to form. The Cr content is preferably 0.1 to 0.3% by mass, and more preferably 0.1 to 0.2% by mass.

[0039] V:0.05~0.3% by mass The addition of V forms fine VSi2 compounds, which promotes the formation and refinement of Al-(Fe, Mn, Cr)-Si crystals. Specifically, VSi2 compounds act as solidification nuclei to form fine CrSi2, which then undergo a peritectic reaction to form Al 13 Si4Cr4 is formed and finally the Al13 Si4Cr4 acts as a solidification nucleus to form fine Al-(Fe, Mn, Cr)-Si crystals. This effect is significant at 0.05 mass% or more, but no improvement in the effect is observed even if the content exceeds 0.3 mass%.

[0040] (2) Optional additive elements Cu:0.2~2.0% by mass The addition of Cu can improve the strength of aluminum alloy castings through solid solution strengthening and age hardening. This effect is significant when Cu is added at 0.2% by mass or more, but when added in an amount exceeding 2.0% by mass, coarse compounds are formed, reducing ductility and corrosion resistance. The amount of Cu added is preferably 0.2 to 1.0% by mass.

[0041] Mg: More than 0.2% by mass and 1.0% by mass or less The coexistence of Mg with Si, an essential additive element, can improve the strength of aluminum alloy castings through age hardening. By adding more than 0.2% by mass of Mg, this effect can be fully achieved, and by adding 1.0% by mass or less, a decrease in toughness can be suppressed. The amount of Mg added is preferably 0.2 to 0.6% by mass.

[0042] Sr:0.005~0.05% by mass Sr has the effect of refining eutectic Si. This effect becomes significant at 0.005 mass % or more, but no improvement in the effect is observed when added in excess of 0.05 mass %.

[0043] Sb:0.005~0.05% by mass Sb has the effect of refining eutectic Si. This effect becomes significant at 0.005 mass % or more, but no improvement in the effect is observed when added in excess of 0.05 mass %.

[0044] Ti:0.005~0.25% by mass Ti has the effect of refining the cast structure (α phase). This effect is significant at 0.005 mass% or more, but no improvement in effect is observed when added in excess of 0.25 mass%. When adding Ti, an Al-Ti-B alloy may be used. In this case, the B content must be 0.05 mass% or less.

[0045] (3) Inevitable impurities Ni, Zn, Pb, Be and Sn are unavoidable impurities and are preferably restricted to 0.05% by mass or less, and other elements are preferably restricted to 0.01% by mass or less.

[0046] 2.Aluminum alloy castings The aluminum alloy casting of the present invention is made of the aluminum alloy for casting of the present invention and is characterized by having finer iron-based compounds. The microstructure and mechanical properties of the aluminum alloy casting are described in detail below.

[0047] (1) Metal structure In the aluminum alloy casting of the present invention, the mode of length of iron-based compounds such as Al-(Fe, Mn, Cr)-Si crystallized particles is 12.5 μm or less. By setting the mode of length of iron-based compounds to 12.5 μm or less, it is possible to fully realize the deterioration of mechanical properties of the aluminum alloy casting caused by the iron-based compounds. It is more preferable that the mode of length of iron-based compounds is 10 μm or less.

[0048] The method for measuring the mode of the length of iron-based compounds is not particularly limited, and various conventionally known microstructure observation techniques may be used. For example, the length distribution of iron-based compounds may be measured using backscattered electron images from a scanning electron microscope (SEM) and appropriate image analysis software. The observation field area is 1.5 mm 2 It is preferable that the above is set.

[0049] Furthermore, since the iron-based compounds in the aluminum alloy casting of the present invention are refined by the formation of VSi2-based compounds, it is preferable that V is present inside the iron-based compounds. When the iron-based compounds contain V, the refinement effect resulting from the formation of VSi2-based compounds can be reliably achieved.

[0050] The method for confirming the presence of V inside the iron-based compound is not particularly limited, and any of various conventionally known elemental analysis methods may be used. For example, confirmation can be performed by SEM-EDS, EPMA, TEM-EDS, STEM-EDS, etc.

[0051] (2) Mechanical properties The aluminum alloy casting of the present invention has excellent tensile properties, including high strength, proof stress, and ductility.

[0052] The tensile elongation is preferably 4% or more, the tensile strength is preferably 230 MPa or more, and the 0.2% proof stress is preferably 170 MPa or more.

[0053] (3) Manufacturing method The aluminum alloy casting of the present invention can be produced by adjusting raw materials so as to have the composition of the casting aluminum alloy of the present invention and casting them by various conventionally known casting methods (sand casting, metal mold casting, gravity casting, low-pressure casting, die casting, etc.). That is, the aluminum alloy casting of the present invention is not limited to those cast by a specific casting method.

[0054] Furthermore, since the aluminum alloy casting of the present invention has a reduced effect of Fe contained as an impurity, it can exhibit excellent yield strength, ductility, and toughness even if the Fe content is increased. In other words, the proportion of scrap material in the raw materials may be increased, and recycled metals can be preferably used from the perspective of building a sustainable society.

[0055] Representative embodiments of the present invention have been described above, but the present invention is not limited to these, and various design modifications are possible, all of which are included in the technical scope of the present invention. [Example]

[0056] Example 1 Raw materials blended to obtain the composition (mass%) shown in Example 1 in Table 1 were placed in a graphite crucible and melted in air at 750°C, followed by degassing at 750°C using a rotary degasser. The melt was then cast into a boat-shaped shape (JIS H 5202) by gravity casting at a casting temperature of 720°C. Next, T7 tempering (solution treatment and stabilization treatment) was performed to obtain Example Aluminum Alloy Casting 1 of the present invention.

[0057] [Table 1]

[0058] Example 2 An example aluminum alloy casting 1 of the present invention was obtained in the same manner as in Example 1, except that raw materials were used that were blended to give the composition shown as Example 2 in Table 1 and no tempering was performed.

[0059] Comparative Example 1 Comparative aluminum alloy casting 1 was obtained in the same manner as in Example 1, except that raw materials blended to give the composition shown as Comparative Example 1 in Table 1 were used.

[0060] Comparative Example 2 Comparative aluminum alloy casting 2 was obtained in the same manner as in Example 1, except that raw materials blended to give the composition shown as Comparative Example 2 in Table 1 were used.

[0061] Comparative Example 3 Comparative aluminum alloy casting 3 was obtained in the same manner as in Example 1, except that raw materials were mixed to give the composition shown as Comparative Example 3 in Table 1 and no tempering was performed.

[0062] Comparative Example 4 Comparative aluminum alloy casting 4 was obtained in the same manner as in Example 1, except that raw materials were mixed to give the composition shown as Comparative Example 4 in Table 1 and no thermal refining was performed.

[0063] [Evaluation test] (1) Microstructure Cubes measuring 1 cm square were cut out from the obtained example aluminum alloy castings and comparative aluminum alloy castings, with their centers located 13 mm from the bottom surface, and the cross sections were buffed to prepare samples for microstructural observation. The microstructures observed with a scanning electron microscope (SEM) for example aluminum alloy castings 1 and 2 are shown in Figures 1 and 2, respectively. The microstructures obtained for comparative aluminum alloy castings 1 to 4 are shown in Figures 3 to 6, respectively. The scanning electron microscope used was a Carl Zeiss ULTRA Plus model.

[0064] The bright (white) areas observed in Figures 1 to 6 are iron-based compounds, which are found to be in the form of fine blocks in the example aluminum alloy castings. Furthermore, the refined iron-based compounds are not distributed continuously. On the other hand, in the comparative aluminum alloy castings, the iron-based compounds are in the form of coarse needles. It was confirmed that the addition of Mn, Cr, and V, when only Mn was added (comparative aluminum alloy casting 3) or when only Mn and Cr were added (comparative aluminum alloy casting 4), hardly refined the iron-based compounds. These results demonstrate that the combined addition of Mn, Cr, and V is essential for the refinement of iron-based compounds.

[0065] The length distribution of iron-based compounds was evaluated from SEM backscattered electron images of the experimental aluminum alloy casting 1, the comparative aluminum alloy casting 1, and the comparative aluminum alloy casting 2. Specifically, the field of view area: 1.77 mm 2 , threshold: area > 10 μm 2 A histogram of the length distribution of iron-based compounds was obtained with a class width of 5 μm. The obtained histogram is shown in FIG.

[0066] Comparing Example Aluminum Alloy Casting 1 and Comparative Aluminum Alloy Casting 2, which have approximately the same Fe content, the most frequent length of the iron-based compounds in Comparative Aluminum Alloy Casting 2 is 15 μm, while it is 10 μm in Example Aluminum Alloy Casting 1, indicating that the iron-based compounds are significantly refined by the combined addition of Mn, Cr, and V. Furthermore, the Fe content of Comparative Aluminum Alloy Casting 1 is low at 0.12 mass%, and coarsening of the iron-based compounds does not progress, but the iron-based compounds of Example Aluminum Alloy Casting 1, which contains 0.42 mass% Fe, are refined to the same extent as those of Comparative Aluminum Alloy Casting 1.

[0067] The element distribution of the aluminum alloy casting 1 was measured using SEM-EDS. The obtained element mapping is shown in Figure 8. The iron-based compound is present in the center of Figure 8, and a fine region where V is concentrated can be observed inside the iron-based compound (the region indicated by the arrow in the figure). The V is due to the formation of VSi2-based compounds.

Claims

1. Si: 7.1% by mass, Fe: 0.40 to 0.42% by mass, Mn: 0.20 to 0.21% by mass, Cr: 0.15% by mass, V: 0.10 to 0.11% by mass, Cu: 0.59 to 0.71% by mass, Mg: 0.34 to 0.35 mass%, the balance being Al and unavoidable impurities; An aluminum alloy for casting characterized by:

2. Si: 7.1% by mass, Fe: 0.40 to 0.42% by mass, Mn: 0.20 to 0.21% by mass, Cr: 0.15% by mass, V: 0.10 to 0.11% by mass, Cu: 0.59 to 0.71% by mass, Mg: 0.34 to 0.35% by mass, Sr: 0.006 mass%, the balance being Al and unavoidable impurities; An aluminum alloy for casting characterized by:

3. The aluminum alloy for casting according to claim 1 or 2, The iron-based compound contains V; Aluminum alloy castings characterized by:

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