Effect of Welding Wire Composition and Post-Welding Heat Treatment on Microstructure and Hardness of New Type α+β Titanium Alloy Welded Joint
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摘要: 针对新型Ti-Al-Mo-V-Cr-Zr-Sn系α+β钛合金板材进行了多层多道钨极惰性气体保护焊接,该方式连接温度低,对母材影响小,且不受材料尺寸大小限制。采用β稳定元素含量不同的两种焊丝制备焊接接头,并对接头的组织形貌和维氏硬度分布进行了研究和分析。结果显示,随着离熔合区的距离减小,母材由魏氏组织逐步过渡到次生α相交叉的网篮组织,热影响区硬度始终大于母材与熔合区的。焊丝中β稳定元素含量较低的焊接接头熔合区的平均硬度约为299.4HV,减小焊丝β稳定元素含量能显著粗化熔合区α片层,降低熔合区平均硬度至275.5HV。对2种焊丝焊接接头进行3种不同制度的焊后热处理,发现热处理温度在650 ℃和700 ℃条件下,熔合区α片层和热影响区次生α相尺寸均无明显变化,但在750 ℃热处理后两者均发生粗化,且焊接接头热影响区的平均硬度降低至与熔合区和母材的接近,两种焊丝焊接接头的平均硬度分别为311.7HV(β稳定元素含量较高)和293.7HV(β稳定元素含量较低)。因此,可以通过改变焊丝元素含量和焊后热处理温度来调整焊接接头微观组织,进而实现对该钛合金焊接接头硬度分布的调控。Abstract: Multi-layer and multi-pass tungsten inert gas shielded welding is used for α+β titanium alloy sheets belonging to the new type Ti-Al-Mo-V-Cr-Zr-Sn series. This method has the advantages of low connection temperature, little impact on thebase metal, and not limited by the size of material. The microstructures and Vickers hardness distributions of the welded joints prepared with two kinds of welding wires with different content of β stable elements are studied and analyzed. As the distance from the fusion zone decreases, the base material gradually changes from the Widmanstatten structure to basket-wave structure with the secondary α phase crossing, and the hardness of the heat affected zone is always higher than that of the base material and the fusion zone. The average hardness of the fusion zone of the welded joint of the welding wire with low β stable element contents is about 299.4HV. Reducing the β stable element contents of the welding wire can significantly coarse the α lamellas in the fusion zone, and the average hardness of the fusion zone reduces to 275.5HV. Three different post weld heat treatments are performed on the two kinds of welded joints. It is found out that there is no significant change in the sizes of the α lamellas in the fusion zone and the secondary α phases in the heat affected zone treated at 650 ℃ and 700 ℃. However, the α lamellas and secondary α phases coarsen when the joint is treated at 750 ℃, and the average hardness of the heat-affected zone of the welded joint is reduced to be close to that of the fusion zone and the base metal. The average hardnesses of the two welded joints are 311.7HV (welding wire with high contents of β stable elements) and 293.7HV (welding wire with low contents of β stable elements). Therefore, the element contents of the welding wire and the post weld heat treatment temperature can be changed to adjust the microstructure to control the hardness distribution of the welded joint.
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