This Verado L6 four-stroke cylinder head for a boat engine coupled with an automotive-style cylinder head with a double water-jacked exhaust manifold was cast in A356 aluminum alloy.

at moderate to fast speeds and feeds. Finishing—Electroplating provides

an excellent fi nish on these alloys. Me- chanical and anodized fi nishes are good. Weldability—Welding of A380.0 and B380.0 is fair for all common types of welding processes. Brazing is not employed. Corrosion Resistance—T ese alloys

have only fair resistance to most corrosive atmospheres, and the protective value of chemical conversion coatings is poor.

Alloys A390.0 and B390.0

T ese companion alloys are hyper- eutectic aluminum-silicon alloys. T e optimum structure of either alloy must consist of fi ne, uniformly distributed primary silicon crystals in a eutectic matrix. T is alloy does not require heat treatment, which may eliminate internal stresses that can cause fatigue failure. T e low coeffi cient of thermal expan-

sion, 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. Castability—For B390.0, the die-

castability rating is good, and relatively thin and intricate sections can be pro- duced. Pressure tightness and resistance to hot cracking are good. Resistance to die soldering is excellent. For A390.0,

permanent mold castability is good. Sand castability is only good because the slower cooling rates adversely af- fect casting microstructure. Pressure tightness and resistance to hot cracking are good. Gating designs for proper di- rectional solidifi cation and feeding are essential for sound castings. Pressure tightness is rated good. Machinability—Tool life when

machining A390.0 or B390.0 is at its best with adequate refi nement of primary silicon crystals. Tools of cast iron cutting grade carbide and M-7 tool steel may be acceptable, but the recommended cutting material is poly- crystalline diamond. Alloys A390.0 and B390.0 require a cutting fl uid in most operations. Many of the com- mercial water-emulsion cutting fl uids are satisfactory. Aside from tool wear- ing, A390.0 and B390.0 alloys have excellent machining characteristics. Chips are short and easy to remove, and high-quality surface fi nishes are generated easily. Weldability—Weldability is fair.

T e best processes are inert gas arc or oxyacetylene welding. Brazing is not recommended. Corrosion Resistance—Resistance

to corrosion is good to excellent, depending on the alloys’ intended environments. Chemical conversion

coatings increase corrosion resistance.

Alloy 535.0 Alloy 535.0 is an aluminum- magnesium 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. Brack- ets, C-clamps and machined parts that need strength, as well as impellers, optical equipment and similar applica- tions requiring a high polish or anod- ized fi nish, are typical uses. In many cases, this alloy has replaced gray iron and malleable iron because it reduces weight without sacrifi cing strength. Castability—T e alloy has fair cast-

ing characteristics and attains its high physical and mechanical properties immediately upon casting. T is fact is important to remember because most high-strength aluminum alloys change properties following age hardening. T ese properties remain constant for 535.0 within the entire range of temperatures from -76 to 225F (-60


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