Developing Empirical Relationships to Predict Grain Size and Hardness of the Weld Nugget of Friction Stir Welded AA7075-T6 Aluminium Alloy Joints

Abstract

High-strength, precipitation-hardening AA7075-T6 alloy is used extensively in aircraft primary structures. Friction stir welding process is an emerging solid state joining process in which the material that is being welded does not melt and recast. The FSW process and tool parameters play a major role in deciding the joint strength. Joint strength is influenced by the grain size and hardness of the weld nugget region. Hence, in this investigation an attempt has been made to develop empirical relationships to predict the grain size and hardness of the weld nugget of the friction stir welded AA7075-T6 aluminium alloy joints. Six factors, five levels, central composite, rotatable design matrix is used to optimize the experimental conditions. The empirical relationships are developed by response surface methodology incorporating tool and process parameters. A linear regression relationship is also established between grain size and hardness of the weld nugget of friction stir welded joints. The weld nugget grain size is related with hardness of the joint. The developed relationships can be effectively used to predict the weld nugget grain size of the joint non-destructively by measuring the weld nugget hardness.