【作者】 张丽娟；

【导师】 刘金水； 李冬珍；

【作者基本信息】 湖南大学 ， 材料工程， 2013， 硕士

【摘要】 汽车轻量化成为21世纪汽车技术的前沿和热点，大量轻质材料在车身上的使用对于整车的轻量化起着举足轻重的作用。对汽车车身多材料结构而言，要求两种不同类型的材料（如钢/铝、铸铁/铝、铝/镁等）进行连接，其中钢/铝性质差异大，易生成脆性Fe-Al金属间化合物，严重影响焊接接头的力学性能。本文选取车用镀锌钢与6016铝合金为研究对象，设计有无粉末填加激光搭接焊试验方案，采用基于密度泛函理论的第一性原理模拟计算与试验相结合的方法，利用卧式金相显微镜、扫描电镜以及Castep商业软件等手段，对Fe-Al金属间化合物脆性行为、接头各区域的金相组织、界面元素分布以及接头力学性能等进行了系统研究，研究结果期望为激光焊接多材料车身结构提供重要理论指导和技术支持。计算了Fe-Al超胞模型Cr、Ni、Mn、Cu、Mo、Pb、Zr合金化前后体系的合金形成热、弹性模量与电子结构，发现富铁的Fe3Al金属间化合物最难形成，而富铝的Fe₂Al₅、FeAl₃、FeAl金属间化合物较易形成，其中FeAl最易形成。相对富铝的Fe-Al金属间化合物，富铁的Fe₃Al金属间化合物金属键较弱，力学性质表现为韧性，而富铝的Fe₂Al₅、FeAl金属间化合物表现为脆性。Cr、Ni易占据FeAl金属间化合物中的Fe位，而Mn、Cu、Mo、Pb、Zr易占据FeAl金属间化合物中的Al位。Zr、Pb、Mn、Mo、Cu降低FeAl脆性，其中Zr、Pb、Mn效果最好，而Ni、Cr增加脆性；由于Mn与Fe有亲和性，与Al有一定互溶性，利于钢/铝界面结合，而Zr细化晶粒，与Al和Fe易形成新相，确定Mn、Zr粉末作为钢/铝激光焊的填加材料。以获得最佳焊缝表面成形性为目标，对1.4mm厚镀锌钢板和1.2mm厚6016铝合金进行填粉激光搭接焊试验，发现填加Mn、Zr粉末，焊接接头平均抗剪强度与没有填加相比，有所提高，其中Zr提高效果明显；粉末的加入，改变了钢/铝界面的元素分布、物相组成及微观组织形态，填加Mn，提高熔池金属的流动性，利于界面结合，而填加Zr，焊缝区晶粒细小，形成新的ZrFe_3.3Al_1.3相，因此填加Mn、Zr，均改善了钢/铝焊接接头的力学性能。更多还原

【Abstract】 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.更多还原