Influence of Diameter Ratio on the Mechanical Properties of Lap Joints in Friction Stir Welding of 2014 Aluminum Alloy

The increased adoption of AA2014 Aluminum alloy within the manufacturing sector can be attributed to its lightweight properties and other attributes that position it as an appealing substitute for steel. Notably, AA2014 Aluminum alloy is employed in the production of components and frameworks for aircraft engines. However, conventional welding techniques do not always seamlessly apply to aluminum alloys due to aluminum's high thermal conductivity, pronounced susceptibility to oxidation, and comparatively low melting point. These characteristics can give rise to challenges such as burn-through and porosity during welding. To tackle these issues, the application of friction stir welding (FSW), a solid-state welding method, has been embraced. In the creation of lap joints, five distinct tools, each featuring a different ratio of tool shoulder diameter (D) to pin diameter (d), ranging from 2 to 4, were employed. An exhaustive evaluation of the mechanical and metallurgical properties of these lap joints was conducted, establishing correlations with the microstructure and microhardness of the stir zone. The outcomes of this investigation disclose that the lap joint crafted using a D/d ratio of 3.0 showcases superior mechanical attributes when compared to lap joints produced at other D/d ratios. This enhancement is attributed to the emergence of finely refined grain structures within the stir zone during the friction stir welding process, coupled with heightened levels of hardness. These elevated hardness levels are identified as the primary contributors to the favorable mechanical and metallurgical qualities observed within the joint.