PRECIPITATION BEHAVIOR OF P M HYPEREUTECTIC AL-SI-CU-MG ALLOYS CONTAINING FE AND NI/

The precipitation phenomena of P/M hypereutectic Al-Si-Cu-Mg alloys wi th and without Fe and Ni addition were investigated by means of DSC, h ardness measurements, TEM and EDX analyses. In order to clarify the ef fects of high density dislocations introduced in the P/M hypereutectic alloys on the precipitation process, an alloy with low Si was produce d by the conventional ingot metallurgy (I/M) and its precipitation kin etics and sequence were compared with those of the P/M alloys. It was found that the addition of Fe and Ni produces intermetallic compounds containing Cu which decrease the volume fraction of GP zones, resultin g in the reduced precipitation hardening. The high density dislocation s introduced during quenching retard the formation of GP zones and acc elerate the precipitation of intermediate phases in the P/M alloys. Th e precipitation sequence of the P/M hypereutectic alloys is markedly i nfluenced by the formation of the stable Q phase (Al5Cu2Mg8Si6) which modifies the Cu/Mg ratio of the matrix.