Some Aspects of Cold Upset Forming of Sintered Aluminum Preforms Using Different Lubricants

Abstract

Cold upset forming and densification features in sintered aluminum preforms using different lubricants were investigated. Cylindrical preforms with initial density 91% of the theoretical one and aspect radio 0.75 were prepared on a 0.1 MN capacity universal testing machine. The preforms were covered with dry fine silica sand and sintered at 520±10°C for 1 h. Cold deformation experiments were carried out in several steps. In general, each compact was subjected to compressive loading in steps of 0.01 MN until fine cracks appeared on its free surface. The experimental data showed that grease exhibits enhanced densification compared to that for MoS2 or graphite lubricants, provided that the initial preform density and aspect ratio are kept constant. The instantaneous strain hardening exponent and strength coefficient of the preforms were calculated and found to reach a peak value when the deformation or packing density were low. Further, they decreased and became constant. The initial geometry of the P/M preforms was shown to play a predominant role in influencing them.