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Everything I have been told says use materials that have been cast already, like lawnmower blocks. Alloys spec'd for casting are not pure aluminum. Crystal structure and growth needs to be controlled while cooling, so elements are added to get a strong casting.
Alloy Selection
There are a number of available alloys to choose from to satisfy individual requirements. Once the casting method is determined, the alloy choice is limited because not all alloys can be used with all casting methods. Sometimes, the alloy that shows the best properties on paper may have production characteristics that make it less desirable on an overall basis than other eligible alloys. Therefore, it is best to consult with a metalcasting facility, which can advise on such factors as availability and relative cost of ingot, production costs and reproducibility of results.
Service requirements also are a key consideration in alloy selection. If high strength is required, heat-treatable alloys must be used. The alloy options can be narrowed further when considering the remaining requirements, such as pressure tightness, corrosion resistance and machinability.
Alloy Designation System—The U.S. Aluminum Association (AA) monitors industry standard specifications for designating aluminum alloys through a numbering system known as the AA “Pink Sheets.†The system designates individual aluminum metalcasting alloys using a three-digit number plus a decimal, which is included on casting blueprints to specify the casting alloy to be used. The standard specifies the chemical composition limits of aluminum alloys and the percentage of each alloying element or an allowable chemistry range. The first digit of the three-digit number system categorizes the casting alloys by groups (or series) according to their major alloying elements.
The balance of the three-digit number identifies the various individual alloys within each alloy series. For example, the 300 series of alloys includes more than 50 individual alloys (319, 356, 357, 380, etc). Some of these individual alloys have multiple variations, all using the same three-digit number. These alloy designations include a letter before the three-digit alloy designation. For instance, variations of 356 are A356, B356, C356 and F356. This letter distinguishes between alloys that fall within the alloy chemistry ranges, but differ slightly in percentages of alloying elements or impurities—such as F357.0, which has a lower minimum level and tighter range for magnesium than 356.0. These variations can determine special casting properties.
The Pink Sheet standard designations apply to aluminum alloys in the form of both castings and ingot, and the single digit following the decimal indicates how the alloy will be used. These designations include:
• XXX.0 = casting;
• XXX.1 = ingot used to make the
casting;
• XXX.2 = ingot used to make the casting with typically tighter chemical limits than the XXX.1 ingot designation.
If AA alloys 356.1 or 356.2, for example, are listed as the alloy specification on casting blueprints, they should define the chemistry of the ingot used to make the cast components, not the final castings. The number XXX.0 for castings includes a chemistry different from the ingot specifications. This leaves room for chemistry changes that can occur during remelting. The addition of casting returns, such as scrap castings, to the charge material also can alter the casting chemistry. The primary difference is that the XXX.0 specifications allow for some magnesium loss (due to burn out) and iron or zinc pickup that may be experienced during processing. The alloy chemistry of the final 356 cast component should fall within the limits of the 356.0 specifications but may not meet the chemical specification for the 356.1 ingot.
Final cast components also should be properly designated. If a blueprint designates 356.1 as the casting alloy, it would be improper to designate the final castings as 356.1. Components should be shipped designated as 356.0 castings.
Metal Matrix Composites—Aluminum metal matrix composites (Al-MMCs) consist of nonmetallic reinforcements incorporated into an aluminum matrix. Reinforcements can be continuous or discontinuous, the most common being silicon carbide. Other reinforcements include boron, alumina and graphite fibers, as well as various particles, short fibers and whiskers. Al-MMCs have better stiffness, wear resistance and thermal conductivity than base aluminum alloys. The American National Standards Institute specifies that Al-MMCs be identified as follows:
Matrix/reinforcement/volume%/form.
Using this formula, a 356 aluminum alloy reinforced with 20% SiC particulate would be designated as 356/SiC/20p.
Alloy Selection
There are a number of available alloys to choose from to satisfy individual requirements. Once the casting method is determined, the alloy choice is limited because not all alloys can be used with all casting methods. Sometimes, the alloy that shows the best properties on paper may have production characteristics that make it less desirable on an overall basis than other eligible alloys. Therefore, it is best to consult with a metalcasting facility, which can advise on such factors as availability and relative cost of ingot, production costs and reproducibility of results.
Service requirements also are a key consideration in alloy selection. If high strength is required, heat-treatable alloys must be used. The alloy options can be narrowed further when considering the remaining requirements, such as pressure tightness, corrosion resistance and machinability.
Alloy Designation System—The U.S. Aluminum Association (AA) monitors industry standard specifications for designating aluminum alloys through a numbering system known as the AA “Pink Sheets.†The system designates individual aluminum metalcasting alloys using a three-digit number plus a decimal, which is included on casting blueprints to specify the casting alloy to be used. The standard specifies the chemical composition limits of aluminum alloys and the percentage of each alloying element or an allowable chemistry range. The first digit of the three-digit number system categorizes the casting alloys by groups (or series) according to their major alloying elements.
The balance of the three-digit number identifies the various individual alloys within each alloy series. For example, the 300 series of alloys includes more than 50 individual alloys (319, 356, 357, 380, etc). Some of these individual alloys have multiple variations, all using the same three-digit number. These alloy designations include a letter before the three-digit alloy designation. For instance, variations of 356 are A356, B356, C356 and F356. This letter distinguishes between alloys that fall within the alloy chemistry ranges, but differ slightly in percentages of alloying elements or impurities—such as F357.0, which has a lower minimum level and tighter range for magnesium than 356.0. These variations can determine special casting properties.
The Pink Sheet standard designations apply to aluminum alloys in the form of both castings and ingot, and the single digit following the decimal indicates how the alloy will be used. These designations include:
• XXX.0 = casting;
• XXX.1 = ingot used to make the
casting;
• XXX.2 = ingot used to make the casting with typically tighter chemical limits than the XXX.1 ingot designation.
If AA alloys 356.1 or 356.2, for example, are listed as the alloy specification on casting blueprints, they should define the chemistry of the ingot used to make the cast components, not the final castings. The number XXX.0 for castings includes a chemistry different from the ingot specifications. This leaves room for chemistry changes that can occur during remelting. The addition of casting returns, such as scrap castings, to the charge material also can alter the casting chemistry. The primary difference is that the XXX.0 specifications allow for some magnesium loss (due to burn out) and iron or zinc pickup that may be experienced during processing. The alloy chemistry of the final 356 cast component should fall within the limits of the 356.0 specifications but may not meet the chemical specification for the 356.1 ingot.
Final cast components also should be properly designated. If a blueprint designates 356.1 as the casting alloy, it would be improper to designate the final castings as 356.1. Components should be shipped designated as 356.0 castings.
Metal Matrix Composites—Aluminum metal matrix composites (Al-MMCs) consist of nonmetallic reinforcements incorporated into an aluminum matrix. Reinforcements can be continuous or discontinuous, the most common being silicon carbide. Other reinforcements include boron, alumina and graphite fibers, as well as various particles, short fibers and whiskers. Al-MMCs have better stiffness, wear resistance and thermal conductivity than base aluminum alloys. The American National Standards Institute specifies that Al-MMCs be identified as follows:
Matrix/reinforcement/volume%/form.
Using this formula, a 356 aluminum alloy reinforced with 20% SiC particulate would be designated as 356/SiC/20p.
