Deformation of SiC Whisker/Zn-22 mass%Al Superplastic Alloy Composites at Elevated Temperatures

Abstract

SiC whisker reinforced composites with Zn-22Al alloy matrix were fabricated by high pressure infiltration and subsequent hot extrusion. Deformation behavior at elevated temperatures was examined under various conditions, and hot compressive forming of the composite ingots into various shaped parts was carried out by using closed dies. Superplasticity was not observed on the composites, whereas the Zn-22Al matrix alloy showed tensile elongation as high as 1200% at 553 K. Metallographic inspection of the elongated specimens revealed formation of voids in the composites. The existence of SiC whiskers as the reinforcement significantly affects deformation and fracture behavior of the composites at elevated temperatures. The strain rate exponent (m-value) of the composites decreased with an increase of whisker volume fraction. At 543 K, the measured m-value was 0.28 for 13% Vf and 0.16 for 20% Vf, while that of the Zn-22Al matrix alloy was 0.44. The highest elongation of the composites was 80% for 13% Vf and 50% for 20% Vf. These elongation values were shown to be high enough to carry out hot forming. Cup- and gear-shaped products of the composites were obtained by compressive forming.