KR20230069152A - aluminum casting alloys - Google Patents

Abstract

The present invention relates to the field of metallurgy, in particular to aluminum-based alloys, and can be used to produce thin-walled complex castings by casting in metal molds, in particular for automotive parts, parts for electronic devices, and the like. The aluminum-based cast alloy of the present invention comprises 1.5 to 5.1 wt % calcium; up to 0.7 wt% iron; up to 1.0 wt% silicon; 0.1 to 1.8 wt % zinc; and optionally 0.2 to 2.5 wt % manganese; 0.005 to 0.1 wt % titanium; 0.05 to 0.14 wt % zirconium; 0.05 to 0.15 wt % chromium, wherein calcium and zinc are present in the structure of the alloy primarily in the form of eutectic particles. The technical result is to provide the desired combination of technical properties as well as corrosion resistance during casting.

Description

aluminum casting alloys

The present invention relates to the field of metallurgy, in particular to aluminum-based alloys characterized by high corrosion resistance. This alloy can be used for the production of thin-walled, complex-shaped castings by casting in metal moulds.

Industrial non-heat-treatable alloys of the A-Si system, such as A413.2 or AK12pch (GOST1583), are characterized by high castability and relatively low levels of strength properties; In particular, the yield strength generally does not exceed 60 to 80 MPa depending on the thickness of the casting. A higher level of strength properties of the casting already in the as-cast condition is provided by the addition of copper; In particular, alloys such as AA383.1 or AK12M2 are known. The increase in mechanical properties in this case is accompanied by a significant decrease in elongation and a decrease in corrosion resistance.

Non-heat-treatable and corrosion-resistant alloys are, for example, Al, such as AMg6L, AMg5K, AMg5Mz (GOST1583), Magsimal ^® 59 (Rheinfelden Alloys), etc., which are characterized by satisfactory machinability in casting, good corrosion resistance, high level of strength properties and elongation. - Includes solid solution alloys based on the Mg system. Disadvantages of this system alloy include high linear shrinkage and insufficient tightness of thin-walled castings.

A combination of high levels of strength properties, elongation and corrosion resistance is achieved in Al-Si alloys with 0.2 to 0.5 wt % magnesium; In particular, AK9 (GOST1583), Silafont ^® 36 (Rheinfelden Alloys), trimal ^® 37 (Trimet) and other alloys are known. Hardening significantly complicates the casting production cycle as it can cause distortion of the casting (especially when water quenching is used), dimensional change and cracking.

The NITU MISIS invention disclosed in patent RU2660492 is known. The material for use in the as-cast condition contains (wt%): 5.4 to 6.4% calcium, 0.3 to 0.6% silicon and 0.8 to 1.2% iron. Disadvantages of the proposed invention include a low relative elongation, not exceeding 2.6%, which limits the use of the material in critical cast parts.

An Al-Ni-Mn cast alloy for structural components in automotive and aerospace applications is known as an alternative to the brand silluminin developed by Alcoa and disclosed in patent US6783730B2 (published Aug. 31, 2004). This alloy produces castings with a good combination of casting and mechanical properties in the case of (wt.%) 2 to 6% Ni, 1 to 3% Mn, 1% Fe, less than 1% silicon, as well as other unavoidable impurities. can be used to produce Disadvantages of the proposed invention include the fact that a high level of casting and mechanical properties is ensured by using high purity aluminum grades and having a high nickel content, which significantly increases the cost of the castings produced. In addition, the proposed material is non-heat treatable over the entire concentration range, which limits its use. At the same time, the corrosion resistance of the casting is significantly reduced in the region of high nickel concentration.

Cast aluminum alloys based on Al-Ni and Al-Ni-Mn systems and methods for producing cast parts from them are known, including Alcoa invention US8349462B2 published on 8 January 2013 and Rheinfelden Alloys GmbH & Co. It is described in KG's application EP2011055318. The invention proposes an alloy composition for casting applications. Typical in the proposed invention is a high nickel content of 1 to 6%, which determines the main drawback - a significant reduction in corrosion resistance. With relatively low nickel and manganese contents, the cast alloy has low level strength properties.

A material based on the Al-Ni-Mn system is known which is disclosed in Russian patent 2478131C2 proposed by NITU MISIS and published on March 27, 2013. The material contains (wt%): 1.5 to 2.5% Ni, 0.3 to 0.7% Fe, 1 to 2% Mn, 0.02 to 0.2% Zr, 0.02% to 0.12% Sc and 0.002 to 0.1% Ce. Castings made of the alloy after annealing (without the use of a quenching operation) are characterized by an ultimate resistance of at least 250 MPa with an elongation of at least 4%. A first drawback of this alloy is its increased tendency to form concentrated porosity, which makes it difficult to achieve high quality and relatively large castings. A second disadvantage is the need to use higher casting temperatures, which are not always achievable in foundry conditions.

The closest material to the proposed one is (wt.%) Al-3.5%Ca-0.9%Mn-0.5%Fe-0.1%Zr disclosed in a publication available at https://doi.org/10.1016/j.msea.2019.138410 It is a material containing -0.1% Sc. The authors of this publication consider the material as a modified alloy, and its process chain precludes water quenching. This publication discloses the obscurity of using the alloys mentioned in the publication for casting and in the as-cast condition. Disadvantages of the proposed invention include the presence of expensive scandium, as well as the need to use heat treatment to achieve the hardening effect of the co-addition of zirconium and scandium.

The object of the present invention is not limited to these, but thin-walled by various casting methods, in particular gravity casting, high pressure casting, low pressure casting, liquid forging, into metal molds that meet the specified requirements and corrosion properties for a set of processes. It is to create new cast aluminum alloys designed to produce castings.

The technical result of the present invention is to provide a given combination of corrosion resistance and process properties in casting.

The technical results are the concentrations of the following alloying elements, wt %:

calcium 1.5 to 5.1

zinc 0.1 to 1.8

steel up to 0.7

silicon up to 1.0

optionally the following groups

manganese 0.2 to 2.5

titanium 0.005 to 0.1

zirconium 0.05 to 0.14

chrome 0.05 to 0.15

It is achieved by proposing an aluminum-based cast alloy having at least one element selected from aluminum and unavoidable impurities - the rest.

In certain versions, calcium and zinc appear in the structure primarily in the form of eutectic particles. Alloys are produced in the form of castings.

Various modifications and improvements are permissible without departing from the scope of the invention as defined by claim 1.

Thanks to the selected combination of alloying elements, the proposed alloy is characterized by a narrow crystallization gap, which in combination with a large amount of the eutectic phase has a good level of casting properties, and thanks to the elements dissolved in the aluminum solid solution - satisfactory in the as-cast state. It provides a good level of strength characteristics. At the same time, with the various combinations of alloying elements selected, corrosion resistance within the claimed area is maintained at a good level.

The basic criterion for the acceptable selection of alloying elements was the formation of the desired structure, excluding the presence of coarse primary crystals and/or coarsening of the eutectic phase; The validity of the concentration range is given below.

Concentrations (wt%) of calcium in the range of 1.5 to 5.1% and zinc in the range of 0.1 to 1.8% provide good casting properties because calcium and zinc mainly form a sufficient amount of the eutectic phase. The main effect of co-introduction of calcium and zinc is the formation of co-eutectic phase Al4(Ca, Zn) in which zinc atoms replace calcium atoms. As a result, the level of strength characteristics is further increased. If the calcium content is below the specified level, this will lead to a decrease in casting properties. If zinc is reduced below the specified level, no significant increase in strength properties will be observed. Calcium and zinc contents above the specified levels will lead to the formation of coarse structures and a significant reduction in mechanical properties.

The iron and silicon content is mainly determined by the purity of the aluminum used to make the alloy. However, iron and silicon can also be used as alloying elements, since silicon in an amount of up to 1.0 wt% is redistributed between the solid solution and the eutectic, which on the one hand due to additional solid solution hardening in the as-cast state reduces the strength properties. This is because it provides an increase and, on the other hand, positively affects the alloy casting properties by increasing the eutectic. With higher silicon content, the morphology of the eutectic phase deteriorates, which generally reduces strength properties. Iron in an amount of up to 0.5 wt% mainly forms phases of eutectic origin, which positively affect the casting properties of the alloy by increasing the amount of eutectic. An increase in the iron concentration above 0.5 wt % may lead to coarsening of the eutectic phase and consequent reduction in mechanical properties.

Manganese in an amount of up to 2.5 wt% is needed to increase strength properties, primarily in the as-cast condition, by providing solid solution hardening. With a manganese content greater than 2.5 wt%, primary crystals of the Al ₆ (Fe, Mn) phase may form in the structure, which may lead to a decrease in mechanical properties. A manganese content of less than 0.2 wt% will not lead to significant solid solution hardening and, consequently, a slight increase in strength properties.

Zirconium and chromium in specified limits (wt%) of 0.05 to 0.14% and 0.05 to 0.15%, respectively, are required to provide solid solution hardening. Lower concentrations of these elements do not lead to significant increases in strength properties in the as-cast condition. Larger amounts will require a higher casting temperature than usual, which will reduce the stability of the casting mold; Otherwise there will be a high probability of forming primary crystals on Al ₇ Cr and Al ₃ Zr, which will not increase the level of mechanical properties from the introduction of these elements.

Titanium in an amount of 0.005 to 0.1 wt % is required to modify the aluminum solid solution. A higher titanium content in the structure may cause the appearance of primary crystals, which will reduce the overall mechanical property level, whereas a lower titanium content will not achieve the positive effect of this element. Titanium may be introduced as a multicomponent ligature such as Al-Ti-B and/or Al-Ti-C, such that the alloy contains boron and a compound with titanium in an amount proportional to the content of the corresponding ligature. It may also contain carbon. Boron and carbon are independent elements and do not significantly affect the mechanical and casting properties of that range. Furthermore, in the presence of titanium, a reduction in the tendency to form hot cracks during casting was noted in some cases.

The following charge materials are alloys (wt.%): aluminum grades A99 and A8, zinc grade C0, calcium as metallic calcium and ligature Al-6Ca, manganese Al-10% Mn as ligature, ligature Al It was used to prepare -10% Zr, Al-10% Cr, and Al-5% Ti.

Example 1

Thirteen alloy compositions were prepared under laboratory conditions to evaluate the effect of alloying elements on structure and properties (Table 1).

[Table 1] - Chemical composition of experimental alloy (wt%)

The content of other elements generally did not exceed 0.05 wt%. The chemical composition of the alloy was selected from conditions to obtain a structure consisting of aluminum solid solution and eutectic components. Specimens were cast by gravity in "separately cast sample" metal molds. The mold temperature can vary from 20 to 60°C. The casting was a 10 mm diameter tensile specimen with an estimated length of 50 mm, which was tensile tested (determination of yield strength, tensile strength and elongation) immediately after casting without machining. The structure of the specimen was evaluated from the specimen head.

[Table 2] - Mechanical properties in as-cast condition (gravity casting into metal mould)

* - Composition in Table 1

Analysis of the structure of the studied alloys revealed that the structure of the considered composition in Table 1 consists mainly of the eutectic phase formed by the aluminum solid solution and the corresponding element. At the same time, calcium and zinc in all experimental alloys appear predominantly in the form of eutectic particles.

Compositions 2, 5 and 12 are preferred because of their good yield strength to elongation ratio for use in the as-cast condition. The most preferred alloy structure using the example of composition 5 (Table 1) is shown in FIG.

Example 2:

The corrosion resistance of the examples of compositions 2, 5, 8 and 11 of the claimed alloy (Table 1) was determined by the following program: 1 cycle - salt spray when spraying a 5% NaCl solution for 8 hours at a temperature of 25 ± 1 ° C. fog) chamber followed by exposure to neutral salt fog under immersion at 35±3° C. without spraying the solution for 16 hours, a total of 7 cycles. Results were evaluated by varying the surface appearance of the specimen and the depth of corrosion damage (metallographic method). An ADC6 type alloy was used as a reference, which is characterized by the highest corrosion resistance among cast aluminum alloys.

A comparative analysis of the results showed that during the test, the surface color of the tested compositions and standards changed from silver to silver-yellow, as well as single surface damage up to 10 microns without significant corrosion damage.

example 3

Casting properties were evaluated using the high temperature brittleness (HB) parameter using "harp casting", the best indicator being to obtain castings with maximum "bar" length (FIG. 2). The propensity for hot cracking was evaluated using alloys 2, 4 and 12 as examples (Table 1). An ADC6 type alloy was used as a comparison. The absence of cracks was noted in alloys 2, 4 and 12 (Table 1), indicating that castings from them were at the level of most Al-Si alloys, in contrast to the ADC6 alloy, where about 40% of the rods fractured starting from their maximum length. is a good indicator in

example 4

To evaluate the mechanical properties of alloy 12 (Table 1), 2 mm thick plates were cast by injection molding (HPDC). Casting was done by vacuuming the mold. The mold temperature was about 150°C. The temperature of the melt was 710 °C. The results of tensile tests on specimens cut from cast plates are shown in Table 3.

[Table 3] - Tensile test results of 2 mm HPDC casting plate (as-cast condition)

Claims (4)

Distribution of the following alloying elements, wt %:
Calcium 1.5 to 5.1
Zinc 0.1 to 1.8
iron max 0.7
Silicon up to 1.0
optionally the following groups
Manganese 0.2 to 2.5
Titanium 0.005 to 0.1
Zirconium 0.05 to 0.14
0.05 to 0.15 chromium
Aluminum and unavoidable impurities - remainder
An aluminum-based cast alloy having at least one element selected from The method of claim 1 wherein the following redistribution, wt %:
Calcium 2.8 to 5.0
Manganese 0.2 to 1.2
iron max 0.5
Silicon up to 1.0
Zinc 0.1 to 1.6
An aluminum-based casting alloy, characterized in that it contains an alloying element of. 3. Aluminum-based cast alloy according to claim 1 or 2, characterized in that calcium and zinc are mainly in the form of eutectic particles therein. The aluminum-based casting alloy according to any one of claims 1 to 3, characterized in that it is produced in the form of a casting.

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