Effect of heat treatment and interlayer on weld strength and microstructure of solid state joints between Cu and Al powder metallurgical preform tubes

Abstract

Solid state joints made between Cu and Al powder metallurgical preforms by cold extrusion were heat treated at various temperatures and for various times with and without an interlayer (Ni) to evaluate the interfacial microstructure and weld strength. The heat treatment conditions were optimised for highest weld strength without deleterious effects in terms of intermetallic compounds, Kirkendall voids, etc. Heat treatment of these joints made without an interlayer resulted in a 40% increase in the strength. However, under some processing conditions different intermetallic compounds and phases were formed during heat treatment without an interlayer. Application of an interlayer in the form of powder allowed partial interdiffusion of metal at the interface and this minor interdiffusion had no influence on the weld strength and microstructure. Finer interlayer particle size increased the weld strength by eliminating physical discontinuities and residual particles at the interface. The heat treatment of Cu–Al joints made using 1 μm Ni powder as the interlayer increased the strength by 82% in comparison with that in the as extruded condition.