Analysis of the Wetting and Diffusion Processes Upon the Contact Alloying of Zn–Cu–Al and Mg–Al Brazing Alloys with AMg3 Alloy

The processes of the contact melting of AMg3 alloy with Zn–Cu–Al and Mg–Al braze solders are studied. The microstructures of cross-sectional views of the alloys after thermal tests are obtained; the processes of melting and crystallization of the AMg3, Zn–Cu–Al, and Mg–Al alloys are investigated and their phase-transition temperatures are determined. The processes of surface erosion of the AMg3 substrate in the process of contact melting of the substrate with Zn–Cu–Al and Mg–Al brazing alloys are studied. The performed investigations demonstrated that intensive diffusion processes carried out at the interface of the brazing alloy and substrate result in deep melting of the substrate both in the presence of an oxide film (for HTS-2000) and upon its absence (Mg66Al34). Contact melting of the brazing alloys results in diffusion effects in the contact area, which is conducive to the formation of complex microstructures, consisting of eutectics, intermetallics, and dendrites of α-Al. The obtained results demonstrate the possibility of controlling the microstructure and properties of the alloying zone through selection of the chemical composition of the brazing alloy and heat-treatment conditions, and also selection of the most preferable fluxing material. The experimental data indicate that the generation of intermetallic phases without the generation of eutectic structures embrittles the area of the brazed joint. Because of this, it is important to select the optimal composition of the brazing alloy and conditions of crystallization, at which highly dispersed eutectic microstructure will be formed.