The Simulation Calculation And Microstructural Performance Research Of Steel/Aluminum Powder Filler Laser Welding

Weight reduction of automobile becomes the frontier and the focus of the vehicletechnology in the21st century. The lightweight materials are being used in the vehiclebody, which plays an important role in the vehicle weight reduction. Two kinds ofmaterials （such as aluminum, steel/aluminum, cast iron/aluminum/magnesium, etc.）have been used in automobile’s body. The big difference between steel and aluminumnot only make the brittle Fe-Al intermetallic compound generated easily, but alsogreatly affect the mechanical properties of weld joints. This article selectedgalvanized steel/6016aluminum alloy as the research objects, and set differentexperiments with adding powder or not, and also apply the first principles calculationwhich is based on density functional theory and experimental methods, such ashorizontal metallographic microscope, the microcomputer control electron universaltesting machine, to research the Fe-Al intermetallic compounds’ brittle behavior,tendency of alloy elements and effect in Fe-Al intermetallic compound. The else weresearch in this paper are the adding elements placeholder types, the microstructure,distribution of interface elements and interface layer, the joint mechanical propertiesand so on. The results bring out from this paper are expected to provide importanttheoretical guidance and technical support to laser welding on automobiles’ body withmulti-material.The formation heat, elastic modulus and the electronic structure of Fe-Al supercell model system and alloying （Cr, Ni, Mn, Cu, Mo, Pb, Zr） system have beencalculated. We found that the most difficult to form is iron rich Fe₃Al intermetalliccompounds, and aluminum rich, such as Fe₂Al₅, FeAl₃, FeAl intermetallic compoundcan be formed much more easily, and Fe-Al was the easiest to form. Iron richintermetallic compound, ductile Fe₃Al, has a weaker metallic bonds than aluminumrich brittle Fe-Al intermetallic compound. Both Cr and Ni occupied the lattice of Fe inFe-Al intermetallic compounds, while Mn, Cu, Mo, Pb and Zr occupied the lattice ofAl in Fe-Al intermetallic compounds.Elements, such as Zr, Pb, Mn, Mo and Cu, can reduce Fe-Al’s brittleness. Inwhich The effects of Zr, Pb, Mn were better. Elements, such as Ni and Cr, can increaseFe-Al’s brittleness. The affinity between Mn and Fe and the intermiscibility betweenMn and Al were good for the interface bonding of aluminum/steel. And Zr not only can fine grains, but also can Zr-Al-Fe form a new phase. So Mn and Zr powders havebeen determined as the padding materials in steel/aluminum laser welding.To get the best weld surface formability, the fiber laser welding test with Mn orZr powder addition is carried out on the DC51D+ZF galvanized steel of1.4mm andthe6016aluminum alloy of1.2mm. The results showed that the average shearstrength of welding joints in the steel/aluminum laser welding was improved byadding Mn, Zr alloy powder, comparing those with no addition. Especially Zr alloypower improving obviously. The steel/aluminum interface element distribution,physical phase composition and microstructure morphology changed with the amountof the alloy powder. The metal molten pool of liquidity was improved by theincreasing of Mn which is beneficial to the interface bonding. The weld area grain isfined with the addition of Zr. A new ductile phase ZrFe_3.3Al_1.3has been formed andwould inhibite the generation of Fe-Al brittle intermetallic compound. Both theincreasing of Mn and Zr can improve the steel/aluminum welding joint mechanicalproperties.