Understanding the effect of hot extrusion on the evolution of microstructure and associated mechanical properties in sintered Al-Cu-Mg alloys

Abstract

A systematic study was carried out to establish a structure-property correlation of Al-Cu-Mg powder metallurgy alloys as a function of extrusion temperature and strain rate. A series of hot extrusion tests were performed on a hydraulic press in the temperature range of 450 °C–550 °C and at a strain rate of 0.1–0.3 s−1. Superior mechanical properties were attained by the uniform distribution of precipitates and dispersoids during extrusion, as witnessed by scanning electron microscopy (SEM), electron backscatter diffraction (EBSD), electron probe micro analyzer (EPMA) and X-ray diffractometry (XRD). The dynamic recrystallization (DRX) was facilitated with the increase in deformation temperature and a decrease in strain rate. Brass {110} 〈112〉, Copper {112}〈111〉 and S {123}<634 > texture components were developed due to extrusion and Cube {100}〈001〉 and Goss {110}<001 > orientations found to be strengthened (with maximum intensities ~7.04 times of any random orientation) due to deformation temperature. The final microstructure of extrudates indicated the presence of α-Al matrix, Al2Cu eutectic structure and Al7Cu2Fe compounds. Primary Al2Cu precipitate dissolved in the matrix with increasing temperature and decreasing strain rate of extrusion. Both dislocation density and residual stress reduced with an increase in extrusion temperature as estimated from nanoindentation experiments following established models. Both yield strength and young's modulus increased after extrusion due to grain refinement, work hardening, precipitate hardening, and dispersion strengthening. However, both decreased with increasing extrusion temperature and decreasing strain rate. The maximum hardness (1305.06 MPa), compressive yield strength (367.24 MPa) and residual stress (1267.609 MPa) were observed in the specimen extruded at 450 °C and 0.3 s−1.