Production of Al–Pb Alloys by Rheocasting

Abstract

A vacuum rheocasting technique in which a solidifying alloy is violently agitated at high speed has been applied to production of some new bearing aluminum base alloys containing 15 to 50 mass%Pb. Rheocast microstructures of Al–Pb alloys have been observed using scanning electron microscopy. Irreqular lead-rich phases in them are uniformly dispersed coexisting with fine eutectics among aluminum-rich primary solid particles formed by fragmentation of dendritic crystals. The torque of a stirrer inserted in the vacuum-melted alloys has been continuously measured during the rotation of stirrer at a speed of 70 s−1 from the beginning to the final stage of solidification. The apparent viscosity of the solidifying alloys, which is evaluated on the basis of the measured values of torque, remains unchanged or decreases gradually during solidification except a rapid change in the initial stage of solidification. The ultimate tensile strength and elongation have been investigated at room temperature and at elevated temperatures. A comparison of the mechanical properties of Al–Pb alloys with those of existing bearing alloys shows that the leaded aluminum alloy is a high cost-performance material.