Study On The Process And Mechanical Properties Of Porous Aluminum Alloy Prepared By Selective Laser Melting Technique

Selective laser melting（SLM） has been developed as a new advanced rapid prototyping technology. Metal parts with advanced properties and complexity shape can be directly manufactured with the SLM technology. Aluminum alloy is a light metal with excellent strength-to-weight ratio. However, some of its inherent properties, i.e. oxidized easily, high reflectivity and thermal conductivity, make it difficult for aluminum alloy parts to be manufactured by SLM. In the present dissertation, SLM method is introduced into the field of porous metals fabrication and porous aluminum alloy were successfully prepared. Phases, microstructures and compositions of the processed porous structures were investigated using XRD, SEM and EDX respectively.The effects of laser processing parameters on microstructural features of the obtained porous structures and their properties were analyzed. The forming mechanism of porous structure with pore forming agents and laser processing conditions is presentated. The micro and macro mechanical properties of porous aluminum alloy were studied by using nano indentation, hardness tester, universal electronic testing machine.Research results show that: the porous ratio of the porous aluminum alloy prepared by selective laser melting technology can be adjusted by the process parameters. The microstructure of porous aluminum alloy is refined and the grain size of layer-layer interface is about 1³um,the grain size of fine grain zone reaches the nanometer level（700nm）. The matrix is composed of α-Al and α-Al+Si, and the Al element is mainly filled in the cellular structure, and the Si elements are mainly located in the cell boundaries. Due to the fine grain strengthening and solid solution strengthening, the micro hardness of the porous aluminum alloy is about 130 HV, increased by about 90% compared with 70 HV hardness value of the traditional cast aluminum. The compressive strength and the elastic modulus of AlSi12 alloy fabricated by casting method are about 17 MPa, 1.1GPa respectively, the compressive strength and the elastic modulus of porous aluminum alloy prepared by SLM technology are about 150 MPa, 3.2GPa respectively, and the compressive strength and elastic modulus of the aluminum alloy were increased by 800% and 190% respectively.There are many defects in porous aluminum alloy prepared by selective laser melting technology, this dissertation analyzes the formation mechanism of porosity and ball and the measures to eliminate the defects.Using AlSi12/TiH₂ powder, porous aluminum alloy with micro-meters size grade porous was prepared by selective laser melting technology. When the laser processing parameters were fixed, with the increase of TiH2 content, the porosity of the porous aluminum alloy increases gradually. TiH2 act as a pore forming agent and providing a protective atmosphere in the process of selective laser melting. Under the high energy laser beam, the TiH2 can provide a protective atmosphere to prevent the oxidation of the metal powder, and guarantee the obtained porous metal with high chemical purity.