Empirical Modeling of Microstructural and Hardness Characteristics of Severely Deformed 7075 Aluminum Alloy in the Semi-Solid State Using Response Surface Methodology

The microstructure and hardness of severely deformed 7075 aluminum alloy by equal channel angular pressing (ECAP) method in the semi-solid state were statistically investigated. The studied responses are grain size, shape factor, and hardness of primary α-Al grains in the semi-solid state. The response surface methodology (RSM) based on Box–Behnken design (BBD) was used to study the influence of ECAP passes, reheating temperature, and holding time on the responses. Mathematical relationships between the input variables and the responses were developed using the analysis of variance (ANOVA). Analysis of residuals versus run number and comparison between the measured and predicted results showed that all three developed models could predict the responses adequately. The calculated percentage contribution of input variables showed that the holding time is the main factor, followed by reheating temperature influenced the microstructural characteristics. The hardness of semi-solid samples was influenced principally by the number of ECAP passes and in the second level by the holding time.