DESIGN OF POWDER-METALLURGY ALUMINUM-ALLOYS FOR APPLICATIONS AT ELEVATED-TEMPERATURES .2. TENSILE PROPERTIES OF EXTRUDED AND CONFORMED GAS ATOMIZED POWDERS

The effects of aging treatments on the tensile properties and microstructure of Al-Cr-Zr-Mn powder metallurgy aluminium alloys prepared from high pressure gas atomised powders were investigated. The alloy compositions were designed to give powders with or without Al13Cr2 intermetallics in the < 45-mu-m size fraction. The Al-5.2Cr-1.4Zr-1.3Mn alloy is typical of the former (concentrated alloy) and the Al-3.3Cr-0.7Zr-0.7Mn alloy of the latter (dilute alloy). The alloys were prepared using a canning/degassing/extrusion sequence or the Conform consolidation process. Measurements of microhardness and electron microscopy were used to correlate the microstructure with the tensile properties. The extruded powders of both alloys exhibited better properties than those of the Conformed powders. A large contribution to the strength of the extruded materials is made by their stabilised fine grain size. The dilute alloys had consistently better ductility. Neither alloy retained its strength after prolonged aging at 400-degrees-C, but the results indicate that a service temperature of 300-degrees-C may be possible.