Modeling For Double-pulse MIG Welded Joints Of Aluminum Alloy Sheet In Automotive Applications Based On Strength Heterogeneity And Morphology

To achieve a well-established industrial layout in the fields of lightweight,lowcarbon,and intelligent development of new energy electric vehicles,the application of aluminum alloy materials has gradually become one of the trends in the new energy electric vehicle industry.Consequently,the special requirements of advanced connection technology are in demand for the properties of aluminum alloys.Doublepulse Metal Inert Gas Welding(Double-pulse MIG welding),which possesses highquality welding seams and welding efficiency,has been widely utilized in the production and manufacturing process of aluminum alloy structures in the vehicle body.However,the non-uniform material strength and morphological changes of aluminum alloy welding joints often become the critical factors restricting the macroscopic structural connection strength.Therefore,higher demands for simulating and modeling the joint region are required.This study focuses on the 2mm-thick aluminum alloy thin plate double-pulse MIG welding joint and explores the non-uniform characteristics and geometric morphology of the joint based on experimental data.Through multi-objective optimization methods and equivalent theories,the joint region’s equivalent expression is realized in terms of strength and geometry.The details are as follows:First,the non-uniform characteristics and morphology features of aluminum alloy thin plate dual-pulse MIG weld joints were quantified and studied.The collected hardness distribution was utilized as an indirect reflection of the non-uniform strength properties in the joint area.Based on this,the joint was divided into five regions.Then,by conducting tensile tests on micro-sized specimens from different regions,the stressstrain relationships of the respective materials in the joint were obtained.These findings reveal the weakening effect of the non-uniform characteristics of aluminum alloy weld joints on the overall structural load capacity.Additionally,the morphological parameters of the joint area were measured,facilitating a comparative analysis of the influence of weld seam morphology features on the ultimate load-bearing capacity of the welded structure.Subsequently,the weld joint was modeled in terms of both strength non-uniformity and weld seam morphology.Addressing the inadequacy of conventional modeling methods in capturing the non-uniformity of joint strength,this paper fittingly derived constitutive model parameters for the material in different regions of the joint,encompassing both the elastic-plastic and damage-failure stages,based on experimental data.Through multi-objective optimization of these constitutive parameters,a fivematerial equivalent model was obtained,capable of comprehensively reflecting the material performance of each region within the joint.To address the limitation of traditional models in capturing the morphological characteristics of the joint,the weld seam region was regarded as a continuous structure composed of discrete elements resembling variable cross-section beams.Leveraging the theory of equivalent variable cross-section beams,these discrete elements were represented as trapezoidal crosssection beams.Furthermore,non-linear spring elements were employed to depict the continuity of the weld seam structure in the welding direction.The combination of these two approaches achieved an equivalent representation of the aluminum alloy dual-pulse MIG weld joint in terms of material distribution and morphological features.This joint model,referred to as the ETS(Equivalent material-Trapezoidal section beam-Spring element)model,encompasses a composite model comprising equivalent materials,trapezoidal section beams,and spring elements for concise expression.Finally,the accuracy and efficiency of the ETS model were validated through numerical simulations of the crashworthiness of the aluminum alloy weld structure in the vehicle body.The target structure consisted of two similarly sized aluminum alloy box-section thin-walled beams joined by welding.Comparative analysis of the simulation accuracy among different joint models was conducted under quasi-static compressive conditions,with the refined solid element model serving as the reference.Furthermore,an exploratory analysis of the simulation performance of each joint model was carried out in low-speed and medium-high-speed collision conditions.In all three conditions,the simulation results obtained using the ETS model exhibited higher overall consistency with the reference object.Additionally,the computational time only experienced a minor increase,demonstrating the capability of this equivalent model to meet the high-precision and high-efficiency engineering requirements across various scenarios.Based on experimental evidence,this paper highlights the necessity of expressing the non-uniform characteristics and morphology of weld joints in the simulation analysis of aluminum alloy weld structures.Consequently,a novel composite model has been established to meet the requirements of accuracy and efficiency.This model provides a fresh perspective and solution for the simulation modeling of aluminum alloy vehicle body weld structures,catering to engineering applications.