The Al-Si-Mg alloy which can be strengthened by heat treatment is widely applied to the key components of aerospace and aeronautics. Iron-rich intermetallic compounds are well known to be strongly influential on mechanical properties in Al-Si-Mg alloys. But intermetallic compounds in cast Al-Si-Mg alloy intermetallics are often misidentified in previous metallurgical studies. It was described as many different compounds, such as AlFeSi, Al8Fe2Si, Al5(Fe, Mn)3Si2 and so on. For the purpose of solving this problem, the intermetallic compounds in cast Al-Si alloys containing 0.5% Mg were investigated in this study. The iron-rich compounds in Al-Si-Mg casting alloys were characterized by optical microscope(OM), scanning electron microscope(SEM), energy dispersive X-ray spectrometer(EDS), electron backscatter diffraction(EBSD) and X-ray powder diffraction(XRD). The electron backscatter diffraction patterns were used to assess the crystallographic characteristics of intermetallic compounds. The compound which contains Fe/Mg-rich particles with coarse morphologies was Al8FeMg3Si6 in the alloy by using EBSD. The compound belongs to hexagonal system, space group P6_2m, with the lattice parameter a=0.662 nm, c=0.792 nm. The β-phase is indexed as tetragonal Al3FeSi2, space group I4/mcm, a=0.607 nm and c=0.950 nm. The XRD data indicate that Al8FeMg3Si6 and Al3FeSi2 are present in the microstructure of Al-7Si-Mg alloy, which confirms the identification result of EBSD. The present study identified the iron-rich compound in Al-Si-Mg alloy, which provides a reliable method to identify the intermetallic compounds in short time in Al-Si-Mg alloy. Study results are helpful for identification of complex compounds in alloys.
The existence of inclusion influences the properties of aluminum alloy castings,from which the castings will face scrapping under severe condition.Great efforts on the inclusions in aluminum alloy were made and many inclusion assessment methods were put forward.However,most of the current methods are characterized by time consuming and expensive equipment cost,which limits the application in aluminum industry.Since the aluminum properties are sensitive to the inclusion,this paper tries to establish a new kind of inclusion assessment method.The inclusions were introduced to aluminum melts by adding aluminum scraps.The samples with different inclusion contents were prepared.The microstructure contained inclusions was observed.The inclusion was automatically identified with an image analyzer by setting different grey threshold value,and the inclusion content was obtained.The image analysis shows that inclusions wreck the continuity of the alloy matrix seriously,and the inclusion area percentage increases with the increasing of aluminum scraps.The high and low polarization measurements were conducted in 3.5 wt% NaCl aqueous solution at the temperature of 25 ℃.The electrochemical parameters of the testing materials,such as corrosion potential E k,corrosion current density I k and the linear polarization resistance R p,were obtained.The polarization measurement results show that the linear polarization resistances decrease,the corrosion potentials move towards more negative direction,and the corrosion current densities increase with the increasing of inclusion content.The theoretical analysis of the inclusion content and the corrosion current density was performed.The existence of inclusions makes the microstructure form corrosion microcells between the alloy matrix and inclusions.The impressed current can accelerate the current velocity or corrosion current density.The regression model of the inclusion contents vs.the corrosion current density was obtained.This model can be used to quantitatively analyze the inclusi
