Investigation of surface roughness effects on microstructural and mechanical properties of diffusion bonding between dissimilar AZ91-D magnesium and AA6061 aluminum alloys

Abstract

The effects of surface roughness were studied on microstructural and mechanical properties of solid-state diffusion bonding between two dissimilar alloys of magnesium AZ91-D and aluminum 6061 by means of hot pressing. Although applied pressure, temperature, and duration of diffusion bonding are known as the most effective parameters, surface roughness can alter the mechanical and microstructural properties remarkably, which is usually neglected. To investigate the effect of surface roughness between 0.06 and 0.15 μm, the width of the diffusion bond in the interfacial transition zone (ITZ) and the presence of intermetallic phases were analyzed. Moreover, microhardness, shear strength, and fracture surfaces were evaluated. The results exhibit that in the applied roughness range, the bond width and the microhardness of the joints improved by increasing the surface roughness of the both metals; however, the shear strength decreased. It may be attributed to more disruption of the oxide films on the metal surfaces in the rougher samples and also increase in the effective interface boundary during the process. Consequently, there would be more chance for aluminum-magnesium contacts, resulting in more diffusion, further formation of brittle intermetallic phases (such as Al12Mg17 and Al3Mg2), and therefore more hardness and less shear strength.