7075铝合金激光熔覆Al-Cr复合涂层

Al-Cr composite coating laser cladding on 7075 aluminum alloy

为了对7075铝合金进行表面强化,采用激光熔覆技术制备了Al-Cr复合涂层,采用扫描电镜(SEM)和光学金相显微镜(OM)观察复合涂层组织结构,采用能谱仪(EDS)进行元素分析,采用X-射线衍射仪(XRD)做物相分析,并测试了复合涂层的显微硬度。结果表明,通过激光熔覆技术制备的Al-Cr复合涂层较为平整,无明显裂纹,与基体形成了良好的冶金结合;复合涂层由金属相(Al和少量的Cr)、陶瓷相(Al_(x)Cr_(y)金属间化合物)共同组成;涂层中的Cr、Al反应有2种机理:液-固反应和固-固反应;金属Al相的作用为粘结涂层与基体、增加涂层的韧性和减少裂纹产生;涂层经历激光作用道次不同,各部位的组织结构和物相组成存在着差异,导致性能发生了变化,涂层的显微硬度沿熔池深度方向呈梯度分布,逐渐下降,其表面硬度最大为977.4HV_(0.5),相对于T6态的7075提高了6.88倍。

In order to strengthen the surface of 7075 aluminum alloy,an Al-Cr composite coating was prepared by laser cladding technology.Scanning electron microscope(SEM)and optical metallurgical microscope(OM)were used to observe the structure of the composite coating.Energy dispersive spectrometer(EDS)was used to elemental analysis,X-ray diffraction(XRD)was used to phase analysis,and the micro-hardness of the composite coating was tested.The results show that the Al-Cr composite coating prepared by laser cladding technology is relatively smooth,without obvious cracks,and forms a good metallurgical bond with the substrate.The composite coating consists of a metal phase(Al and a small amount of Cr)and a ceramic phase(Al_(x)Cr_(y)intermetallic compounds).There are two reactions mechanisms of Cr and Al in the coating:liquid-solid reaction and solid-solid reaction.The Al phase of the metal plays the roles to bond the coating to the substrate,increase the toughness of the coating and reduce the generation of cracks.The coating experiences different laser passes,so there are differences in the structure and phase composition of each part,which leads to changes in performance.The microhardness of the coating is gradually distributed along the depth of the molten pool and gradually decreases.The surface hardness is maximum 977.4HV_(0.5),which is a 6.88 times increase compared to 7075 in the T6 state.