Effects of intermetallic particles on cavitation during superplastic forming of aluminium alloy

An Al-4.6%Mg-1.5%Mn-0.27%Fe alloy was specially processed with friction stir processing followed by cold rolling. Half of the sheet thickness contains a large number of blocky or irregular-shaped Al-6(Mn,Fe) coarse intermetallic particles, while the other half, smaller and more spherical ones. The particle-induced cavitation upon uni-axial tension at 475 degrees C with 2 x 10(-4)-2 x 10(-2 )s(-1) strain rates was investigated. The density of nuclei for cavities was estimated based on quantitative image analysis of the particles, and the strain controlled growth rate, calculated assuming the cavities are nucleated before or in the early stage of straining. The number, size and morphology of intermetallic particles are found to control the cavitation by determining the nucleation rate, but the strain controlled growth rate appears unaffected.