The creep properties of a system of 3 to 5 per cent Cu in A1 alloys containing hard particles of CuAl2 were investigated throughout a temperature range of 350 to 578 K. The results supplemented with additional tensile-test data show that these properties are primarily dependent on the volumetric mean free path of the CuAl2 particles and independent of minor variations in composition andheat-treatment. The creep stress was found to correlate with the creep rate-temperature parameter Z = ϵ˙seΔH/RT. Above ln Z = ln (ϵ˙seΔH/RT) = 46.0 and below ln Z = 27.5 the finer dispersions are superior, whereas over the intervening range of Z-values the coarser dispersions are superior. The energy for activation ΔH, was found to be a constant of about 37,000 cal per mol.

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