Static and fatigue behaviors of rotary friction welded AA7075 joints

In this paper mechanical properties (hardness and tensile strength) and fatigue behavior of weld joints in rotary friction welding (RFW) of AA7075 aluminum alloy were studied at varying tool rotational speeds of 370, 540, 800 and 1200ârpm. The experimental methods used in this study included macro and microstructural examinations, microhardness measurements, tensile tests and fatigue tests. The results showed that increasing rotational speed reduced the width of dynamic recrystallization zone (DRZ) due to axial forging force accompanied by a significant increase in the hardness, especially at interface. In contrast, the high heat input due to increased rotational speed caused heat affected zone (HAZ) to become wider leading to degradation in mechanical property. As a result, this region is the weakest part in RFW joints. It was found that the best weld joint was produced at 1200ârpm in which the friction heat was sufficient to produce metallurgical bonding with less flash and burn-off length. Under tensile tests, the static fracture occurred at the region between dynamically recrystallized zone (DRZ) and thermomechanically affected zone (TMAZ). Furthermore, results of fatigue tests showed that the strength of the welding joint was lower than its AA7075 base metal and the fatigue crack was controlled by mainly microstructure. It was found that the fatigue crack was initiated at TMAZ near DRZ which had a high concentration and it propagated through HAZ which provided easy passage for the growing crack. © 2024 Author(s).