Microstructure And Mechanical Properties Of Rapid Solidified Al-Si-Cu-Mg Sintering Aluminum Alloy

Al-Si alloy has the properties of high specific strength, low thermal expansioncoefficient, high wear resistance, has been widely applied to the aerospace,automotive and electronics field. However, in the high silicon aluminum alloyproduced by traditional casting process, the primary silicon is too coarsely to splitthe substrate, as a consequence, the mechanical properties are weakened seriously.In this study, Al-Si alloy is prepared by Al-Si-Cu-Mg rapid solidified powderthrough the process of cold pressing technology and N2atmosphere sintering. Thesecond phase precipitated in the sintering process and after heat treatment, theinfluence of size and distribution of dispersed second phases on mechanicalproperties Al-Si-Cu-Mg alloy are investigated.The premixed commercial powder used in this work(named Ecka Alumix231)is provided by Ecka Granules, has a chemical composition ofAl-15.4Si-2.6Cu-0.57Mg. The average size of powder is85.94μm. XRD analysis,SEM observation and TEM analysis conducted on the powders in differentsize(38-75μm、75-106μm、>106μm)indicate the powder is mostly formed by α-Al，β-Si，θ-phase（CuAl2），Q-phase（Cu2Mg8Si6Al5）.In the smaller size particles, theprimary silicon crystals are found surrounded by the Al-Si eutectic-like structure,the intermetallic θ-phase and Q-phase form a web-like structure that surrounds theeutectic-like Al-Si zone in the master alloy. In the larger particles, a huge number ofsecond phases dispersed in the master alloy. From the TEM observation, we can seeplate shaped θ’-phase distributed along the β-Si grain boundaries, G.P.zonesdispersed through the matrix.Al-Si-Cu-Mg alloy is prepared by cold pressing and sintering. The workingpressure for cold pressing is330MPa, sintering temperature is545℃, sinteringtime is40min, protective atmosphere is N2. Plate shaped G.P. zones, θ’-phase andθ-phase and strip shaped Q-phase dispersed throughout the matrix, leading to thestrengthening of the alloy. Hardness, Ultimate tensile strength of as-sintered A011sample are86.82HV,177MPa.An artificial age-hardening heat treatment(T6) is developed to improve themechanical properties of Al-Si alloy. The solutionizing temperature is520℃,solutionizing time is1h, followed by a water quench to ambient. Age-hardeningtemperature is160℃,Age-hardening time are6h,8h,10h.After heat treatment, Sigrain grew up, the number of precipitates increased. The hardness of the alloy isincreased with the age-hardening time.