(Today's post is a review of an article that was published in the Jul/Aug 2016 issue of METALCASTING DESIGN & PURCHASING. You can read the entire article "Aluminum Characteristics by Alloy" here.)
Inside the aluminum family, the various alloys exhibit marked and unique manufacturing characteristics that distinguish themselves. Generally, cast aluminum should be used for applications that require lower weight and structure without necessarily needing high strength at elevated temperatures. To help you choose the best fit, the following breaks down the castability, machinability, finishing tendencies, weldability and corrosion resistance of common aluminum casting alloys (Table 1).
Alloy 206 is a high strength aluminum alloy often used for structural casting components in automotive and aerospace applications where high tensile and yield strength are required and· moderate elongation is acceptable. Typical applications include gear housings, cylinder heads, turbines and impellers, and other applications where high strength at elevated temperatures is necessary for service life.
Alloys 319.0, A319.0, B319.0 and 320.0
Alloys 319.0 and A319.0 exhibit good castability, weldability, pressure tightness and moderate strength arid are stable in that their casting and mechanical properties are not affected by fluctuations in impurity contents. Alloys B319.0 and 320.0 show higher strength and hardness than 319.0 and A319.0 and generally are used with the permanent mold casting process. Characteristics other than strength and hardness are similar to those of 319.0. Typical applications for sand castings of these alloys include internal combustion and diesel engine crankcases, gasoline and oil tanks, and oil pans. Permanent mold cast components include water-cooled cylinder heads, rear axle housings and engine parts.
Alloy 356.0 has excellent casting characteristics (Table 2). Permanent mold castings of this alloy are used for machine tool parts, aircraft wheels and hand wheels, pump parts, tank car fittings, marine hardware, valve bodies and bridge railing parts, as well as for aileron control sectors, rudder control supports, fuselage fittings and fuel tank elbows for airplanes and missiles. Automotive applications include miscellaneous castings for trucks and trailers, spring brackets, cylinder heads, engine blocks, passenger car wheels and transmission cases. Uses for sand castings of356.0 include flywheel housings, automotive transmission cases, oil pans, rear axle housings, brackets, water-cooled cylinder blocks, various fittings and pump bodies. This alloy is used in various marine applications in the T6 condition where pressure tightness and/or corrosion resistance are major requirements.
Due to lower levels of impurities, alloy A356.0 has greater elongation, higher strength and considerably higher ductility than 356.0. Typical applications are airframe castings, machine parts, truck chassis parts, aircraft and missile components, and structural parts requiring high strength.
Alloys A380.0 and B380.0
These alloys are used for producing general purpose die castings. They have good mechanical properties and are used to make housings for lawn mowers and radio transmitters, air brake castings, gear cases and air-cooled cylinder heads.
Alloys A390.0 and 8390.0
These companion alloys are hypereutectic aluminum-silicon alloys. The optimum structure of either alloy must consist of fine, uniformly distributed primary silicon crystals in a eutectic matrix. This alloy does not require heat treatment, which may eliminate internal stresses that can cause fatigue failure. The low coefficient of thermal expansion, high hardness and excellent wear resistance of these alloys make them suitable for internal combustion engine pistons and blocks and cylinder bodies for compressors, pumps and brakes.
Alloy 535.0 is an aluminummagnesium alloy possessing a high, stable combination of strength, shock resistance and ductility. It is suited for parts in instruments and computing devices where dimensional stability is of major importance. In addition to the high ductil-
ity and tensile strength of 535.0, the Charpy impact is 10-12 lbs., which makes it suitable for shock-resistant applications. In addition, this alloy doesn't require heat treatment. Brackets, C-clamps and machined parts that need strength, as well as impellers, optical equipment and similar applications requiring a high polish or anodized finish, are typical uses. In many cases, this alloy has replaced gray iron and malleable iron because it reduces weight without sacrificing strength.
Alloy 712.0 is employed when a combination of good mechanical properties without heat treatment is needed. It also shows good shock and corrosion resistance, machinability and dimensional stability. No distortion is exhibited when 712.0 is heated. After brazing, the alloy will regain its original strength by natural aging. The alloy is used for marine castings, farm machinery, machine tool parts and other applications in which the part must have good strength or impact resistance.