ALUMINUM BRONZE

Foundry practice for aluminum bronze must be carefully controlled. The elimination of oxide inclusions is one of the principal problems. Agita­tion of the metal, whether in the furnace or during casting, can lead to serious results.
It is important to design the gating so that the metal enters and fills the mold cavity without turbulence. Gaes and runners should be wide and thin to help the alloy skim itself before entering the .mold. Pouring must be conducted so that the metal rises very slowly in the mold.
After the casting is poured, slow cooling should be avoided or "self-annealing", a. type of casting embrittlement found in low iron-aluminum-copper alloys, may take place. Castings should be removed from the mold as soon as they are solid enough to handle without distortion.If the casting
are large, it may help to spray them with water after they have been removed from the sand. Chilled castings usually cool rapidly enough so that no additional cooling is necessary. If no other method is available, self-annealing effect.,> may be overcome by heat treating the castings, or by using an a110y with higher iron and nickel content. Aluminum bronzes with 4% iron or high nickel content are less subject to "self-annealing".
Although aluminum bronze is usually thought to have a high solidification shrinkage, experi­mental data show that shrinkage is considerably less than for most copper-base casting alloys. The apparent shriI1kage problem is probably associated with the very narrow solidification range, which
gives the metal similar freezing characteristics to pure metal. As a result, piping is a problem and large, carefully placed risers are frequently necessary.