镀锌钢-6016铝合金激光焊接组织性能与第一性原理计算

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

采用基于密度泛函理论的第一性原理方法,计算Fe8Al8及(Fe7X)Al8(X=Pb,Sn,Ti,Cu,Mn,Si,Zn)超胞模型的弹性模量与电子结构,在分析合金化元素改善FeAl金属间化合物力学性质的基础上,选取降低脆性效果较好的Cu和最好的Pb,对1.2 mm厚DC56D+ZF镀锌钢和1.15 mm厚6016铝合金平板试件进行加入中间夹层Cu和Pb的激光搭接焊试验。结果表明:FeAl金属间化合物为脆性相,其电子结构根源在于Fe的sd态与Al的sp态存在电子轨道杂化,为明显的共价键特征;FeAl合金化后,脆性降低,相应脆性由低到高的顺序为(Fe7Pb)Al8、(Fe7Sn)Al8、(Fe7Ti)Al8、(Fe7Cu)Al8、(Fe7Mn)Al8、(Fe7Si)Al8、(Fe7Zn)Al8、Fe8Al8,Pb合金化降低脆性效果最好,激光搭接焊加入中间夹层Pb,钢侧母材与焊缝界面区由母材侧较大晶粒和焊缝的细小晶粒交错形成,熔池金属与母材铝之间没有明显的分界线,焊接接头界面熔合良好;与未加夹层相比,加入中间夹层Cu和Pb后,焊接接头力学性能提高,其中Pb的作用优于Cu的,试样断口均具有韧性断裂特征。

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.