Effect of reinforcement size on low strain yielding behaviour in Al–Cu–Mg/SiCP composites

The low strain yielding behaviour of SiCp reinforced Al–Cu–Mg alloy matrix composites with varying reinforcement sizes was investigated. Three different sizes (1.4, 15.8 and 62.8 μm) of SiCp were used to produce metal matrix composites (MMCs), namely, MMC1, MMC16 and MMC63, respectively, by employing a proprietary powder metallurgy technique. Matrix alloy was also produced in a similar manner for comparison and designated as Control. All materials were heat treated to peak aged condition and subjected to a controlled strain deformation of 1.5% in both tension and compression. The yield stress at 2.5×10−4 offset strain, termed as ‘actual yield’, of all the MMCs was significantly lower than that of Control during both tensile and compressive deformation. The actual yielding in all the MMCs and Control occurred at lower stress levels in compression than in tension. The observed results were attributed to the distribution of residual stresses in the matrix of MMCs generated due to the large difference in coefficient of thermal expansion between the matrix and the reinforcement.