Laser lap welding structural properties and first-principle computation of zinc-coated steel and 6016 aluminum alloy

The elastic moduli and electronic structure were calculated by the first-principle method based on the density functional theory for Fe8Al8 and(Fe7X)Al8(X=Pb,Sn,Ti,Cu,Mn,Si,Zn) supercell model.Analysis on improving the mechanical properties of FeAl intermetallic compounds was done,Cu and Pb were considered as better elements to reduce the brittleness of FeAl intermetallic compound.The laser lap welding experiments with the Cu or Pb metal sandwich addition were carried out with the DC56D+ZF galvanized steel of 1.2 mm-thick and the 6016 aluminum alloy of 1.15 mm-thick.The results show that the FeAl compound is the brittle phase which attributes to the electron orbit hybridization between the states of Fe-sd and Al-sp with obvious covalent bond characteristics.The brittleness of FeAl compound is reduced with the addition of alloying elements,and the brittleness order from low to high is as follows:(Fe7Pb)Al8,(Fe7Sn)Al8,(Fe7Ti)Al8,(Fe7Cu)Al8,(Fe7Mn)Al8,(Fe7Si)Al8,(Fe7Zn)Al8 and Fe8Al8.The laser lap welding experiment with the Pb metal sandwich addition shows the weld joint contact surface with better fusion based on the fact that the metal of steel side and welded joint frontal zone is made of big crystal grain of metal and tiny crystal grain of welded joint,and the boundary between the pool and metal of aluminum is not obvious.The mechanical properties of the welded joints are improved with the Cu or Pb metal sandwich addition,and the specimen fracture characteristic is ductile.