Production Characteristics The physical properties of custom
alloys are a primary consideration in formulating new chemistries. How- ever, the casting characteristics also need to be factored into the equation. One study evaluated the ways die
casters and designers could optimize aluminum die casting alloys to en- hance mechanical and physical prop- erties without sacrificing castability. The study, “Casting Characteristics
Cast in a customized 319 aluminum alloy, this turbocharger impeller for diesel engines provides up to 50% cost savings over forged and machined impellers.
year. Reducing the amount of alloy lowered raw material costs and led to annual energy savings of 45 million BTUs. (The die caster in this case buys molten metal, so the energy savings do not include energy for melting. Plants that melt ingot would show greater energy savings.) In another example of custom
alloy use, a marine manufacturer reduced the copper content in an aluminum alloy for improved corro- sion resistance. Thermalloy, originally a custom alloy, has a significantly higher
thermal conductivity than previously used die casting alloys. Now, Ther- malloy is a standard specification in products requiring high thermal conductivity, such as heat sinks. Custom alloys also can achieve equivalent casting properties at a lower cost. One die caster increased the iron, zinc and magnesium in an aluminum 380-style alloy and reduced the cost of the metal by $0.03/lb., which yielded significant savings because the die caster was using 150 million lbs. of aluminum alloy per year.
of Aluminum Die Casting Alloys,” by Makhlouf Makhlouf and Diran Apelian, Worcester Polytechnic Insti- tute, Worcester, Mass., evaluated five experimental alloys and commercial A380 alloy to determine four casting characteristics (Table 1): • die soldering (the adhering of mol- ten metal to portions of the die)
• fluidity (the ability of molten metal to flow)
• sludge formation (the accumulation of oxidized elements heavier than the base metal that settle to the bot- tom of a crucible or furnace)
• machinability. The study determined that the
five experimental alloys did not show problems with die soldering and sludge formation. The fluidity test suggested the alloys are fairly comparable to A380 alloy. From the microstructure analysis, it was also predicted that these alloys should not have machining problems, pro- vided that appropriate machining
Aluminum 380 is used in a variety of applications without customization, including in the rear-view mirror mount shown here. 44 Metal Casting Design anD PurChasing MarCh/aPril 2010
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