Correlation between weld nugget grain size, weld nugget hardness and tensile strength of friction stir welded commercial grade aluminium alloy joints

Friction stir welding process (FSW) 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 was made to develop empirical relationships to predict the grain size and hardness of weld nugget of the friction stir welded AA1100 aluminium alloy joints. Linear regression relationships are established between grain size and hardness of the weld nugget and weld nugget hardness and tensile strength of FSW joints. The developed relationships can be effectively used to predict the weld nugget grain size and tensile strength of the joint non-destructively by measuring the weld nugget hardness.

► FSW is a solid state joining process. It eliminates melting related defects.
► Empirical relationships were developed to predict the grain size, hardness and tensile strength.
► The joint strength can be predicted, if the hardness is known. It eliminates non-destructive test.