Effect of Major Alloying Elements Zn and Mg on Microstructure and Microhardness of AA7075 Alloys and their Composites

Prachi Mittal, Ishu Verma, Amit Tomar, Jayanta Kumar Mahato

Pre-print pages 1-14

DOI: https://doi.org/10.62753/ctp.2025.05.2.2

keywords: metal matrix composites, AA7075 alloy, stir casting, microstructure, microhardness

abstract The present research work focuses on studying the effect of the major alloying elements on the microstructure and hardness of 7xxx series aluminium alloys and their composites. AA7075 aluminium alloy was used as the base material and different weight percentages of alloying elements zinc (Zn) and magnesium (Mg) were added at ratios 1:1, 2:1 and 3:1 to the base material. Afterwards, the modified aluminium alloys were used as matrix materials for the fabrication of aluminium alloy matrix composites (AAMCs) by adding different weight fractions of silicon carbide (SiC) as reinforcement material. Both the alloys and the AAMCs were fabricated by means of stir casting. XRD, SEM and EDX analysis of the modified aluminium alloys and their composites were carried out. Microstructures of the modified aluminium alloys and AAMCs were observed and the grain sizes were measured according to ASTM standards. Hardness tests of the fabricated specimens were carried out using Vickers microhardness testers and the hardness values were measured utilising the integrated software. It was observed that equiaxed grain structures were formed in both the modified Al alloys and their composites, indicating successful fabrication by means of the casting process; however, the average grain sizes of the fabricated specimens are dependent on the combination of wt% of reinforcement and the composition of the Al alloys. Interestingly, a positive correlation with the weight percent ratio of Zn and Mg in the AA7075 was observed, indicating the potential for fine-tuning of the mechanical properties through proper selection of the alloying elements. It was also observed that the microhardness of the AAMCs fabricated with the modified Al alloys exhibits consistent improvement with an increasing weight fraction of SiC reinforcement, irrespective of the weight percentage ratio of the added Zn and Mg combination.