Precipitation sequence in a SiC/Al-Mg₂Si alloy composite material

The precipitation sequence of an Al-1.0mass%Mg₂Si composite material having 8 vol.% SiC particles was investigated by Vickers micro hardness and specific electrical resistivity measurements, and by TEM observation. The formation of GP zones was suppressed in the composite material and its age-hardenability was reduced. Distribution of precipitates in the composite material was coarser and their size was larger than that in the Al-1.0mass%Mg₂Si alloy (base alloy). Some types of precipitates in the composite material were not similar to those found in the base alloy but were similar to those in an Al-1.0mass%Mg₂Si alloys with excess silicon (the excess Si alloy). Especially, the metastable phases in the composite material aged at 473 K belonged to the type-A, type-B and type-C precipitates, which are typical metastable phases in the excess Si alloy, instead of the β′ phase that is a typical metastable phase in quasi-binary Al-Mg₂Si alloys. The dislocations had little effect on the aging process of this composite material, because of the small number of dislocations introduced by the quenching after solution treatment.