High-Performance Be-Al Casting Alloys

Investment casting is a near net shape manufacturing process that typically reduces both the amount of alloy and machining time needed to produce a part. The reductions in these two areas frequently lead to significant decreases in the total cost of the part. Materion has developed procedures for the investment casting of three Be-Al alloys (AlBeCast® 910, 920 and 930). These alloys are composed primarily of Be and Al, and also contain smaller concentrations of other elements (Si, Ge, Ni, Ag, Co and Sr). The Be and Al have very little solubility for one another. Also, they have quite different solidification temperatures (1285 and 660 C respectively). As a result Be-Al alloys solidify with a large mushy zone and form two phases, one being Be and the other Al. In general the alloying elements are selected to improve the mechanical and casting properties of the Al phase, although they also have an impact of the Be phase. X-ray dot maps of alloy cross sections show that the Si, Ge, Ag and Sr tend to stay in the Al phase whereas the Ni and Co forms solid solutions with both the Be and Al. The addition of Ag has the largest impact on the strengths of the alloys due to its tendency to form a Widmanstatten plate, δ’, phase with the Al. Additions of Co and Ni increase strength but also produce a large decrease in thermal conductivity. The high concentrations of Be in these alloys result in high specific modulus values.