激光选区熔化成形含钛6061铝合金的显微组织与力学性能

Microstructure and mechanical property of titanium-containing 6061 aluminum alloy prepared by selective laser melting

激光选区熔化(selective laser melting,SLM)成形6061铝合金易形成粗大的柱状晶和热裂纹。采用低能球磨组装修饰法制备TiH_(2)/AA6061铝基复合粉末,采用激光选区熔化技术制备含钛6061铝合金试样,分析不同TiH_(2)添加量对试样显微组织和力学性能的影响。结果表明:添加1%TiH_(2)(质量分数,下同)即可使合金熔池边界形成连续的等轴晶区,平均晶粒尺寸从59.8μm减小到2.53μm,粗大的柱状晶粒和裂纹被抑制,添加1.5%TiH_(2)时,SLM试样的粗大柱状晶组织绝大部分消失。显微组织转变归因于Ti元素增强成分过冷以及原位反应形成L12-Al_(3)Ti形核质点,该质点与铝基体形成共格界面,具有较强的异质形核作用,显著促进Al基体柱状晶向等轴晶转变及晶粒细化。经激光选区熔化成形后,添加1%TiH_(2)的试样抗拉强度为274 MPa,屈服强度为238 MPa,断后伸长率为18%。

The 6061 aluminium alloy is a heat treatable reinforced aluminium alloy containing magnesium and silicon as its main alloying elements.It is commonly used in the aerospace and automotive industries due to its excellent mass to strength ratio and high thermal conductivity,but is particularly susceptible to the formation of coarse columnar crystals and thermal tearing,particularly during SLM processing.TiH_(2)/AA6061 aluminium-based composite powders were prepared by the low-energy ball milling assembly modification method,and the titanium-containing 6061 aluminum alloy specimens were prepared by selective laser melting technique.The microstructure and mechanical properties of the samples with different TiH_(2) contents were systematically investigates.The results show that the addition of 1%TiH_(2)(mass fraction,the same below)results in the formation of a continuous equiaxed crystal zone at the alloy melt pool boundary,the average grain size decreases from 59.8μm to 2.53μm,and the coarse columnar grains and cracks inhibit,and with the addition of 1.5%TiH_(2),the coarse columnar grains of the SLM specimens inhibit completely and only a few small columnar grains exist.The microstructure transformation is attributed to the enhancement of the constituent undercooling by Ti elements and the in-situ reaction to form L12-Al_(3)Ti nucleation particles,which form a coherent interface with the Al matrix and have a strong heterogeneous nucleation effect,thus significantly promoting the transformation from columnar to equiaxed crystals and grain refinement of the Al matrix.After selective laser melting,the tensile strength of 6061 aluminum alloy with 1%TiH_(2) addition is 274 MPa,the yield strength is 238 MPa,and the elongation after break is 18%.