Microstructure Evolution of AZ91 Alloy Processed by Twin Parallel Channel Angular Extrusion Technique

In the present study, multi-step processing of an as-cast AZ91 alloy was conducted using twin parallel channel angular extrusion. The first step was conducted at 340 degrees C to increase the workability, and the next steps were implemented at lower temperatures. Microstructure evolution was investigated via optical microscopy and scanning electron microscopy techniques. Additionally, x-ray diffraction analysis was used to determine the dislocation densities. Moreover, the mechanical strengths are evaluated in terms of indentation hardness values. The results indicate that processing for three passes, implemented, respectively, at temperatures of 340, 300, and 250 degrees C, gives the most uniform and the finest microstructure, where the average grain size is reduced to approximately 2 mu m and the dislocation density to 0.61 x 10(14) m(-2). Besides, the average hardness value for such a processing condition reaches 104 Vickers, indicating an improvement of similar to 48% in comparison with the initial value. The improvement is due to the different strengthening mechanisms verified by hardness modeling based on the empirical relations.

Automated summary

In this study, multi-step processing of an as-cast AZ91 alloy using twin parallel channel angular extrusion was investigated. The results showed that processing for three passes at temperatures of 340, 300, and 250 degrees C resulted in the most uniform and fine microstructure with reduced grain size and dislocation density. The average hardness value also significantly improved compared to the initial value.