Hot deformation behavior and strain compensation constitutive model of equiaxed fine grain diffusion-welded micro-duplex TC4 titanium alloy

In this work, two-stage diffusion bonding of micro-duplex TC4 titanium alloy was carried out to study the flow behavior and constitutive models of the bonding joint and the base metal after the same thermal cycling during the hot forming process. Microstructure and mechanical properties test were used to verify the good quality of the equiaxed fine grain diffusion-welded TC4 alloy. Quasi-static tensile experiment was carried out at temperatures ranging from 750–900 °C and strain rates of 0.0001–0.1 s⁻¹. The joint showed the weak dynamic recovery at strain rates of 0.01–0.1 s⁻¹ and temperatures of 750–850 °C. At strain rates of 0.0001–0.001 s⁻¹ and temperatures of 850–900 °C, the flow stress of joint presented steady-state characteristics. Different deformation conditions lead to the remarkable difference of dynamic softening performance between the joint and heat-treated base metal, but the flow stress in elastic and strain hardening stages exhibited similar behavior. The strain compensated Arrhenius-type constitutive models of TC4 joint and heat-treated base metal were developed respectively. The fifth-order polynomial functions between the material property correlation coefficients and strain were obtained. The models have shown good correlation, with correlation coefficient values of 0.984 and 0.99. The percentage average absolute relative error for the models were found to be 10% and 9.46%, respectively.     

2524与7150铝合金激光焊T型接头的组织与性能

介绍了2524与7150铝合金激光焊T型接头优化的工艺参数,并研究了T型接头在优化工艺下的显微组织与力学性能,进行金相分析、显微硬度测试与接头拉伸试验。结果表明:优化工艺下焊缝没有裂纹、气孔,金相组织晶粒细小、致密,焊缝区域的硬度最低;T型接头x方向的拉伸强度达到384 MPa,z方向的拉伸强度为236 MPa。     

Effect of adding Nb foil on joint properties of laser fusion welding for TC4 titanium and 7075 aluminum alloy

It is difficult to gain effective Ti-Al fusion welding joints due to their differences in thermal properties and the appearance of brittle Ti-Al Intermetallic Compounds (IMCs). The experiments of laser fusion welding for TC4 titanium and 7075 aluminum alloy were carried out, temperature field and ductility/brittleness, as well as chemical potential of elements, were calculated, and the effect of adding Nb foil on mechanical properties of the weld was also investigated. The results suggested that Nb atoms tend to diffuse toward Al side, which is conducive to the participation of Nb in the metallurgical reaction and contributes to forming the Ti-Nb-Al IMC layer at the interface. As the thickness of Nb foil increases, the tensile-shear force of joint climbs first but then declines, and reaches the highest value of 1663 N with 0.10 mm-thickness Nb foil, representing 58.38% enhancement compared with the non-added one. Adding Nb foil slows down the heat transfer as a blocker, and thus both the melting amount of Al and the mixing area of Ti and Al decrease. In addition, Nb alloying reduces the brittleness of the Ti-Al compound. Hence, the joint properties of titanium/aluminum are improved with the addition of Nb foil.