Heat treatment of cold-sprayed C355 Al for repair: microstructure and mechanical properties

Cold gas dynamic spraying of commercially pure aluminum is widely used for dimensional repair in the aerospace sector as it is capable of producing oxide-free deposits of hundreds of micrometer thickness with strong bonding to the substrate, based on adhesive pull-off tests, and often with enhanced hardness compared to the powder prior to spraying. There is significant interest in extending this application to structural, load-bearing repairs. Particularly, in the case of high-strength aluminum alloys, cold spray deposits can exhibit high levels of porosity and microcracks, leading to mechanical properties that are inadequate for most load-bearing applications. Here, heat treatment was investigated as a potential means of improving the properties of cold-sprayed coatings from Al alloy C355. Coatings produced with process conditions of 500 °C and 60 bar were heat-treated at 175, 200, 225, 250 °C for 4 h in air, and the evolution of the microstructure and microhardness was analyzed. Heat treatment at 225 and 250 °C revealed a decreased porosity (~ 0.14% and 0.02%, respectively) with the former yielding slightly reduced hardness (105 versus 130 HV0.05 as-sprayed). Compressive residual stress levels were approximately halved at all depths into the coating after heat treatment, and tensile testing showed an improvement in ductility

The effect of cold work on the precipitation and recrystallization kinetics in Al-Sc-Zr alloys

Scandium plus zirconium additions to aluminum offer potent alloy strengthening opportunities with enhanced kinetic stability at elevated temperatures, attributable to a favorable sequence of trialuminide precipitation events which occur. This work examines the additional variable of prior cold work on precipitate aging kinetics, and on the recrystallization of the underlying aluminum matrix. Al-0.07Sc-0.08Zr (at%) alloys have been cast, swaged, and isochronally aged over a range of temperatures to quantify hardening response and degree of recrystallization. Cold-worked specimens are compared to as-cast variants; the recrystallization response of the alloy is compared to pure aluminum. These data demonstrate the expanded and optimized properly space attainable via microstructural response to thermomechanical processing