Analysis of Structures at the Boundary of Contact Melting Al–Mg–Mn and Zn Based Alloys

The processes of contact melting of the AMg6 (Al-6%Mg-1%Mn) alloy with Zn–Cu–Al solder and the model Zn–Al alloy, as well as the structure of the contact fusion zone, are studied. Samples were obtained in two stages. At the first step, the solder was mechanically applied (tinned) to the surface of the AMg6 plates. Аt the second step, the resulting composite samples were subjected to heat treatment with a varied exposure time in the liquid state. According to the data of metallographic and X-ray diffraction analyses, as well as differential scanning calorimetry, it was shown that already at the tinning stage the active interaction between Zn and Al occurs, which leads to the formation of a developed microstructure in the joint zone. The presence of copper in the solder HTS-2000 reduces the melting point of the Zn-Al alloy by 30-40°C and improves the conditions for contact interaction with the grade AMg6 matrix. Active diffusion of zinc ensures the formation of an extensive melting zone during heat treatment, while zinc-rich areas during crystallization contain the Zn₅Cu intermetallic phase, which prevents the formation of intermetallic Zn_xMg_y compounds, which does not lead to embrittlement of the contact zone.