Bonding mechanisms in cold spray deposition of gas atomised and solution heat-treated Al 6061 powder by EBSD

TL;DR

This study investigates how solution heat-treatment of gas atomised Al 6061 powder affects microstructure and bonding in cold spray deposits, revealing that dislocation accumulation at interfaces enhances particle bonding.

Contribution

It introduces a new mechanism linking microstructural homogenisation after heat-treatment to improved bonding in cold spray deposits.

Findings

Heat-treated powder shows large stress-free grains.

Dislocation accumulation occurs at interfacial zones.

Enhanced particle bonding due to dislocation-driven subgrain rotation.

Abstract

The heat-treatment of a number of gas atomised aluminium alloys prior to cold spraying recently showed that the resultant microstructural modification was accompanied by an improvement in deposition; however, the relationship between the microstructural homogenisation occurring after recrystallisation and the increase in deposition efficiency and particle-particle bonding had not been investigated. In this study, AL 6061 gas atomised feedstock powder, before and after solution heat-treatment, was cold sprayed and these materials were charaterised using electron backscatter diffraction. The solution heat-treated Al 6061 powder showed large stress-free grains as opposed to the as-atomised feedstock powder which exhibited a homogeneous distribution of misorientation and lattice defects throughout the particles, whereas the coating produced from solution heat-treated powder showed an accumulation of dislocations in the interfacial zones. For the first time, a mechanism was proposed where this phenomenon was attributed to localised deformation of the heat-treated particle's exterior due to the dissolution of precipitates in the intermetallic network. The accumulation of dislocations in the interfacial area enhanced the rotation of subgrains to accomodate the plastic deformation, thus improving the particle-particle bonding.