Effect of rotation speed on nugget structure and property of high rotation speed friction stir welded Al-Mn aluminum alloy

Abstract

High rotation speed friction stir welding is a promising low-force welding technique that enables the application of friction stir welding on in situ fabrication and repair. High rotation speed friction stir welding experiments (above 3000 rpm) were conducted on an Al-Mn aluminum alloy. The effect of rotation speed on nugget structure and property was investigated in order to illuminate the process features. The results indicate that a notable increase of nugget size occurs at high rotation speeds of 5000–8000 rpm. With increasing rotation speed, the thermal effect is firstly strengthened and then achieves a steady state. The microstructure evolution is more sensitive to welding temperature as rotation speed varies, and thus, the evolution trends of nugget structure morphology (grain size and substructure distribution density) with rotation speed resemble that of welding temperature. Increasing rotation speed above 4000 rpm effectively improves the nugget hardness due to the enhancement of strain hardening.