Microstructural characteristics of joint region during diffusion-brazing of magnesium alloy and stainless steel using pure copper interlayer

A novel joining method, double-stage diffusion-brazing of an AZ31 magnesium alloy and a 304L austenitic stainless steel, was carried out using a pure copper interlayer. The solid-state diffusion bonding of 304L to copper was conducted at 850 °C for 20 min followed by brazing to AZ31 at 520 °C and 495 °C for various time. Microstructural characteristics of the diffusion-brazed joints were investigated in detail. A defect free interface of Fe-Cu diffusion area appeared between the Cu alloy and the 304L steel. Cu-Mg reaction products were formed between AZ31 and Cu alloys. A layered structure including AZ31/Cu-Mg compounds/Cu/Fe-Cu diffusion layer/304L was present in the joint. With time prolonging, the reduction in the width of Cu layer was balanced by the increase in the width of Cu-Mg compounds zone. Microhardness peaks in the zone between AZ31 and Cu layer were attributed to the formation of Mg-Cu compounds in this zone.