Abstract
A range of Al-Mg-Li-C MMCs (25 vol.-% of 3 μm SiC particles) were produced by mechanical alloying and powder processing at Aerospace Metal composites, Farnborough. Upset forging trials were conducted at 350 and 550°C and 0.01 and 0.1 S-l. No SiC particle cracking or wedge cracking at grain boundary triple points was observed. Forging at 550°C caused some edge cracking and a coarser grain structure. Large billets of varying composition were forged to ∼15 mm thick plate at 350°C and 0.0l S-l or 550°C and 0.l S-l. Monotonic testing showed the MMCs to exhibit high stiffnesses at moderate strength levels but rather low ductility and fracture toughness. Significant strengthening was found to accrue from dispersion hardening (C content) and solid solution strengthening (Mg and Li solutes). A link was found between lower proof stress and coarser grain structure after forging at 550°C. Fracture toughness K1C was found to decrease with increasing yield strength which was attributed to higher strain concentrations in the smaller crack tip plastic zone.
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