Optimization on hardening process parameters of alumnium alloy 7075 based composites using gra approach
Authors: R Ashok Raj , A Santhosh Prakash , D Antony Prabu , S Vijayan 
Published: October 2023

Abstract
Aluminum Metal Matrix Composites (AMMCs) play a vital role in various industries, including aerospace, aviation, maritime, transportation, and automotive, owing to their remarkable mechanical strength, resistance to corrosion, and tribological performance. The age-hardening process for AA7075-based Metal Matrix Composites is essential to meet specific performance requirements, improve material properties (enhancing mechanical properties, tailoring material performance, improving wear resistance, reducing weight, enhancing corrosion resistance, extending service life), and enhancing the overall suitability of these materials for a wide range of demanding applications. The objective of this study is to improve the mechanical and tribological characteristics of AA7075-based composites by utilizing the age-hardening process, rather than introducing additional reinforcements to the base material. Aluminium Alloy 7075 (AA7075) is selected as the matrix material due to its significant need for improvement in mechanical, corrosion, and tribological properties. Nano zirconium dioxide (ZrO2) is chosen as the reinforcement to meet the property requirements of AA7075 for various applications The composites comprising AA7075 alloy and varying weight percentages of ZrO2 (x = 0, 5, 10, 15, and 20) are fabricated using the stir casting method. The fabricated composites are subjected to tensile strength and density tests to determine the optimal combination of AA7075-based composites by employing the Archimedes principle and a Universal Testing Machine, respectively. The manufactured AA7075-based composites were subjected to EDAX and SEM tests to determine the wt% presence of elements of reinforcement and matrix material by employing the S 3000 - HITACHI model. The stir-cast AA7075-based composites were further subjected to hardening under different conditions to enhance their required properties. Age hardening was performed with the help of a Muffle furnace. The input parameters for hardening were age-hardening temperature (200, 300, and 300 °C), hardening duration (90, 180, and 270 min), and cooling environments (Furnace, water, and atmosphere). The chosen response parameters were micro hardness and wear loss. The microhardness and wear resistance of these composites were assessed using a Vickers hardness tester and a Pin-on-Disc testing apparatus. The optimization was carried out using Grey Relational Analysis (GRA). The confirmation test was conducted to determine density, Ultimate Tensile Strength (UTS), micro hardness, and wear loss. The AA7075/15 wt% ZrO2 composite exhibited a uniform distribution of zirconium dioxide in the AA7075 matrix material among the other manufactured composites. The AA7075/15 wt% ZrO2 exhibited higher density of 2.889 g cm−13 and UTS of 316 MPa than other combinations of AA7075 composite materials. Increasing the heating temperature and duration enhanced the micro hardness and wear resistance. Higher micro hardness and wear resistance were obtained with furnace cooling compared to other cooling environments. The optimized age-hardening process parameters are hardening temperature (400 °C), hardening duration (270 min), and cooling environment (Furnace cooling). The enhanced mechanical and tribological properties result from precipitate formation and density enhancement. The confirmation test for the combination specimen yielded higher density, UTS, micro hardness, and lower wear loss values, which are 2.896 g/cm3, 325 MPa, 138 HV, and 27 mg, respectively.