Abstract
In this paper, the effect of different shapes of tool pin on the plastic flow of 2024-T6 aluminum alloy during friction stir welding was studied. In order to observe the plastic flow of materials more clearly, we chose the method of friction stir welding of dissimilar materials, considering the different corrosive characteristics of aluminum alloys made of different materials when exposed to the same corrosive liquid. By studying and comparing the temperature field, macro and microstructure, microhardness and tensile properties of welded joints, the results indicated that the metal in the weld nugget zone (WNZ) mainly came from the base metal of the advancing side, the thread being the driving force of the downward movement of the FSW plastic metal. The deep groove thread tool pin had the strongest ability to drive the metal downward. The conical cam thread tool pin had the strongest stirring effect on materials and the best metal fluidity. The macroscopic morphology, microstructure, mechanical properties and fracture morphology of different joints were analyzed, and the results showed that all joints could form an excellent union, with an onion ring pattern appearing in cross-section. The minimum grain size of the WNZ formed by the conical cam thread stirring head was 7~12 μm; the hardness was least at the junction of the heat affected zone (HAZ) and the thermo-mechanically affected zone (TMAZ). However, the hardness of the weld formed by the conical cam thread at this point was higher than that of other stirring heads; the tensile strength of all joints was more than 80% of the BM, and the maximum tensile strength of the joint welded by the conical cam thread tool pin was 364.27 MPa, accounting for 86.73% of the base metal (BM). The elongation after break was 14.95%. Tensile fracture morphology analysis showed that all joints were fractured by plastic fracture.
Highlights
Publisher’s Note: MDPI stays neutral2024 aluminum alloy is an Al-Cu-Mg series hard aluminum alloy, which has been used in modern industry due to its excellent comprehensive mechanical properties and high temperature creep resistance [1–3]
The heat generated by the shoulder is the main heat source during the Friction stir welding (FSW) process
We found that the peak temperature of the measured point on the advancing side (AS) was slightly higher than that of the retreating side (RS), irrespective of the shape of pin used, and the temperature difference was about 15~30 ◦ C
Summary
Publisher’s Note: MDPI stays neutral2024 aluminum alloy is an Al-Cu-Mg series hard aluminum alloy, which has been used in modern industry due to its excellent comprehensive mechanical properties and high temperature creep resistance [1–3]. Compared with traditional fusion welding methods, FSW overcomes welding defects, such as porosity and heat crack in the joint, and has high welding efficiency, no alloy element burning, small deformation and other advantages [7–9]. Studies [10] have shown that the main factors affecting the quality of weld joints in the FSW process include welding speed, rotation speed, shoulder pressure, and shape of the tool pin. In the process of FSW, the pin is an important factor affecting material flow. A reasonable structure design of the pin is conducive to better material flow and mixing in the FSW process, and achieves better performance of welded joints [11]. Many researchers have studied the effect of the tool pin on the microstructure and properties of FSW joints of aluminum alloys. Md.Reza-E-Rabby et al [12] conducted FSW tests on the 6061-T651 with regard to jurisdictional claims in published maps and institutional affiliations
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