Texture, Microstructure, and Surface Mechanical Properties of AZ31 Magnesium Alloys Processed by ECASD

Abstract

The current work presents the results on Mg AZ31B alloy sheets subject to four passes using Equal Channel Angular Sheet Drawing (ECASD) at various temperatures (25, 100, and 200 C). Textures are determined by laboratory X-ray diffraction and EBSD. EBSD allows the evaluation of the evolution of crystal sizes in function of the distance to the surface and the presence of twinning. Twinning is evident by the analysis of the textures, which show mainly two components, one due to the spin induced by the shearing of ECASD and the other one as a direct product of twinning. Micro-hardness, by Knoop tests on the lateral face of the sheets, are performed, allowing the determination of the influence of SPD on the hardness from surface to surface, going through the center of the sheet. Almost 50% increase on hardening, with respect to the non-processed material, is obtained near to the surface after four and six passes. The effectiveness as a hardening technique declined after the first four passes.

Heterogeneity of strain path, texture and microstructure evolution of AA6063-T6 processed by Equal Channel Angular Sheet Extrusion (ECASE)

“…After the first ECASE pass, the biggest hardness increments were registered in the regions close to the edges (more intense shearing zones) than in the sheet core (center) where the hardness values are quite similar to the values for the material before deformation. A similar behavior was observed in the study of Fandiño et al [21] with a magnesium alloy processed by ECASE. The lower overall hardness increase observed in this study in comparison with other studies, such as the one from Khelfa et al [22] for an Al-Mg-Si alloy processed by ECAP, can be mainly attributed to the lower amount of deformation introduced with each ECASE pass (~0.3 with this ECASE die against 0.66-1.0 for the most common ECAP dies).…”

Equal channel angular sheet extrusion (ECASE) as a precursor of heterogeneity in an AA6063-T6 alloy

“…After the first pass, it can be seen how the main hardness gains were obtained in regions closer to the edges instead of the sheet core, where the hardness is quite similar to the initial material (T6 condition). However, as the deformation continued the hardness values were getting more homogeneous along the material thickness, as in the study of Fandiño et al [33] with a magnesium alloy. The lower hardness increase observed in this study can be mainly attributed to both the lower amount of deformation introduced with each ECASE pass and the initial state of the starting material (T6 condition), since it is well know that the main hardening contribution of this alloy is coming from the precipitation effect as has been indicated in other studies [34].…”