Optimization analysis of Nd: YAG laser self-fluxing welding of Titanium alloy/stainless steel dissimilar metal by RSM

摘要

The tensile load, weld depth-to-width ratio and IMCs layer thickness response value of 304 stainless steel / Ti6AI4V titanium alloy dissimilar metal joint under Nd: YAG pulsed laser self-fluxing welding condition were obtained by using the RSM of Box - Behnken design experiment. A multivariate nonlinear regression mathematical model was established by using the stepwise regression method to screen out the significant factors affecting the responses. The variance analysis and regression analysis show that the regression model probability Delta Prob > Delta F is less than 0.001, which indicates that the regression equation can simulate the real surface well. The results show that there is a linear proportional relationship between the tensile load and the weld depth-to-width ratio/the IMCs layer thickness. The influence of the process parameters on the tensile load has a very complex interaction. Different from the similar metal welding, to obtain the maximum limit strength requires longer pulse width, smaller pulse repetition rate and welding current. The maximum tensile load is 705.008N under the optimum parameters of welding current 122A, pulse width 15ms and pulse repetition rate 2HZ. Under the optimal parameters, there is no macroscopic crack in the welded joint, and the evenly distributed IMCs along the welding interface exhibits 3 layers of color distinctly different microstructure. The welds interface generates alpha-Ti, TiFe, TiFe2 and a small amount of TisCr(7)Fe(17) IMCs. The order of precipitation is Ti5Cr7Fe17, C14_Laves (TiFe2) and BCC_B2 (TiFe). The brittle cleavage fracture of the welded joints occurs under normal stress. The fracture occurs in the fusion zone, breaking along the TiFe and TiFe2 IMCs layers, and the fracture forms many secondary cracks.