High temperature tensile deformation behavior of new heat resistant aluminum alloy

This study attempted to investigate the high temperature tensile deformation behaviour of new Al-1%Mg-1.1%Si-0.8%CoNi heat resistant aluminium alloy. New aluminium alloy strengthened by Co-Ni based phase was manufactured by using powder ball milling and continuous casting, based on the alloy design & preliminary test. High temperature tensile tests were conducted at various temperatures from 298K to 723 K. OM, SEM, EPMA, XRD, FIB and HR-TEM equipments were used to analyse microstructure, phases, and fracture surface. Microstructure of the new alloy mainly consisted of Al matrix and Co-Ni based phases (1̃8 μm). The Co-Ni based phase was analyzed and confirmed as (Ni, Co)₃Al₄ having incoherent interface with matrix. In high temperature tensile results, the new aluminium alloy didn't show significant decrease (19.6%) of strength with increasing temperature (723 K), suggesting totally different behaviour vis-a-vis conventional A319 alloy (87.0% decrease of T.S.). Fractography observation results of new alloy represented the ductile fracture mode with dimples. Voids were mainly initiated at Co-Ni based strengthening phases. It was apparently observed that the strengthening effect of the (Ni, Co)₃Al₄ could be still maintained at high temperature of 723 K. The deformation mechanism of this alloy was also discussed.