Preparation Of In-situ MgAl₂O₄/Al Composites And Grain Refinement Effect

Grain refinement is an effective way to improve the mechanical properties of aluminum alloy.Grain refinement methods and processes have always been the focus of aluminum alloy research.In recent years,high potential Mg Al₂O₄ refiner has become a research hotspot.Solving the agglomeration problem of Mg Al₂O₄and giving full play to the heterogeneous nucleation of Mg Al₂O₄ are important research contents of such refiners.In this paper,the effects of oxygen source and process parameters on the in-situ synthesis of Mg Al₂O₄ and its heterogeneous nucleation in aluminum alloy were systematically studied,the feasibility of improving the wettability and dispersibility of Mg Al₂O₄ by a simple low-cost process was investigated to improve the refining effect(1)MgAl₂O₄ was synthesized in Al-Mg melt using Cu O as oxygen source by direct melt reaction method.The effects of copper oxide particle size,stirring temperature,copper oxide content and magnesium content on the refining effect of Mg Al₂O₄ were studied.The optimal process parameters of in-situ synthesis of Mg Al₂O₄ and its heterogeneous nucleation were explored.The results show that the factors affecting the heterogeneous nucleation of Mg Al₂O₄ are as follows:magnesium content,copper oxide particle size,stirring temperature,and copper oxide content.The influence of magnesium content,copper oxide particle size and stirring temperature is larger,and the influence of copper oxide content is smaller.The optimal process parameters for in-situ synthesis of Mg Al₂O₄ with high nucleation rate are as follows:copper oxide particle size 5?m,stirring temperature675?,copper oxide content 0.15wt%,magnesium content 1wt%.The ultimate tensile strength,elongation and elastic modulus of Al-Mg alloy increased from84.1MPa,14.2%and 3497MPa to 101.2MPa,18.3%and 4085MPa,with the increase of 20.1%,28.9%and 14.4%,respectively.(2)MgAl₂O₄/Al composites were synthesized by melt direct reaction at three different reaction temperatures(900°C,950°C,1000°C)using Cu₂O as oxygen source.The reaction mechanism of in-situ formation of Mg Al₂O₄ by Cu₂O and the refinement mechanism of Mg Al₂O₄ were discussed.The results show that the optimum reaction temperature for preparing Mg Al₂O₄/Al composite by Al-Mg-Cu₂O system is 1000°C,and the grain size of the aluminum alloy is the smallest.The ultimate tensile strength of the corresponding Mg Al₂O₄/Al composite increases from 53.8 MPa to 74.4 MPa,which is about 38%higher than that of the pure aluminum sample.