Effect of Process Parameters on Microstructure and Mechanical Properties of Friction Stir Welded Cast Nickel Aluminum Bronze Alloy (C95800)

In the present study, Friction Stir Welding (FSW) of Nickel Aluminum Bronze (NAB) alloy was carried out by varying the axial load, rotation speed and welding speed rate. Micro-structural analyses of these samples revealed the different grain sizes and shapes of the various zones. Hardness and tensile strength tests were carried out for the samples welded at different conditions such as axial load, welding speed and rotational speed. Grain refinement in the weld nugget zones was achieved for all welding conditions. The refined grains in weld nugget zone (WNZ) make a main contribution to the increase of mechanical properties of FSW welded NAB alloy. The microhardness of the stir zone and Thermo-Mechanically Affected Zone (TMAZ) was found to be higher than that of the base metal. Transverse tensile strength of weld joint was higher than that of the base metal. On the other hand, a lower or similar tensile strength value compared to the base metal was seen from other variable welding parameters. This was due to the tunnel defect in the welded nugget zone. ANOVA test result was used for finding out the contribution of the process parameter.本研究针对镍铝青铜（Nickel Aluminum Bronze, NAB）合金开展搅拌摩擦焊（Friction Stir Welding, FSW）试验，通过调整轴向载荷、旋转速度及焊接速率三个工艺参数完成焊接制备。对所得试样开展显微组织分析后发现，不同区域的晶粒尺寸与形貌存在显著差异。针对不同工艺参数（轴向载荷、焊接速度、旋转速度）下焊接得到的试样，分别进行了硬度与拉伸强度测试。所有焊接工艺条件下，焊核区（weld nugget zone, WNZ）均实现了晶粒细化；焊核区的细化晶粒是搅拌摩擦焊镍铝青铜合金力学性能提升的核心原因。研究结果显示，搅拌区与热机械影响区（Thermo-Mechanically Affected Zone, TMAZ）的显微硬度高于母材，且焊接接头的横向拉伸强度同样优于母材。而其余可变焊接参数对应的试样，其拉伸强度则低于或与母材相当，该现象源于焊接焊核区存在隧道型缺陷。本研究通过方差分析（ANOVA）试验结果，明确了各工艺参数对焊接过程的贡献占比。