DSC measurement and HRTEM observation of precipitates in an Al-1.6 mass%Mg2Si alloy

Precipitation sequence in an Al-1.6 mass%Mg2Si alloy was investigated by DS C measurement and HRTEM observation, Four exothermic peaks (A, C, D and E) and one endothermic peak (B) were obtained when samples were heated at 10 K /min. Precipitates were confirmed when samples aged to the temperature of e ach peak were observed using HRTEM, and were classified into several types. Products in the region between peaks A and B were classified as GP zones. Precipitates between peaks B and C were classified as the random-type preci pitates. Precipitates at peak C were classified as the parallelogram-type p recipitates. Precipitates at peak D were classified as metastable phase bet a '. Precipitates at peak E were classified as equilibrium phase beta. Alth ough there have been many reports that the beta " phase is formed at peak C , this was not observed in the present study, rather random-type precipitat es were observed. The hardness of samples heated to various temperatures wa s measured. The temperature that resulted in maximum hardness corresponded to the temperature that yielded the maximum amount of random-type precipita tes.