Effect Of High-Pressure Solidification And Aging Treatment On Microstructure And Conductivity Of Al-Si-Fe-Mg Alloy

Al-Si alloy is one of the most commonly used materials in various fields such as automotive and aerospace and has a wide range of applications in the field of high strength and high heat dissipation components.The research on aluminum alloys has focused on mechanical properties,corrosion and wear resistance for a long time.In the field of aluminum alloy heat dissipation,there is few research to simultaneously enhance the thermal conductivity and mechanical properties of Al-Si alloys in particular.Therefore,in this paper,the effects of high-pressure solidification and aging treatment on the microstructure,thermal conductivity and mechanical properties of Al-11.7Si-0.4Fe-0.2Mg alloy,which was previously developed,were investigated.The transformation mechanism of the Fe-rich phase,the precipitation behavior of the solute atoms,and the mechanism of the change in the thermal conductivity of the alloy were further explored.It was found that the Al-11.7Si-0.4Fe-0.2Mg alloy solidified at different pressures was mainly composed ofα-Al andβ-Si phases by XRD analysis.The microstructure observation and energy spectrum analysis of the alloy showed that the Fe-containing intermetallic compounds in the matrix wereα-Al₈Fe₂Si phase,β-Al₅Fe Si phase andπ-Al₈Fe Mg₃Si₆phase at atmospheric pressure.Theπ-Al₈Fe Mg₃Si₆phase disappeared in the alloy at a solidification pressure of 1GPa.Theα-Al₈Fe₂Si phase disappeared during solidification at high pressure of 3 GPa,while theδ-Al₄Fe Si₂phase was formed.The eutectic Si in the Al-Si-Fe-Mg alloy under atmospheric pressure solidification was promiscuously distributed in the matrix with coarse and long needles,while a small amount of bulk primary Si existed due to the effect of nonequilibrium solidification.The increase in the melting point of the alloy under high pressure led to the transformation of the typical eutectic structure to a hypoeutectic structure,and the morphology of the eutectic Si phase changed from a needle-like structure to a short sheet-like structure.The edges of eutectic Si passivated under 1 GPa solidification,and both the number and size of primary Si phases decreased.Under the solidification pressure of 3 GPa,the eutectic Si in the Al-Si-Fe-Mg alloy was significantly refined and distributed in a network at the primaryα-Al grain boundaries,and the primary Si phase disappeared.The solid solution degree of Si inα-Al matrix raised from0.76 at.%to 5.60 at.%with increasing solidification pressure.The mechanical properties of the alloy were significantly improved by solid solution strengthening and second phase refinement under high pressure solidification,while the thermal conductivity of the alloy was remarkably reduced due to the scattering effect of lattice distortion on electrons.Theα-Al₈Fe₂Si andβ-Al₅Fe Si phases were formed by the peritectic reaction L+Al₁₃Fe₄→α-Al₈Fe₂Si and the ternary eutectic reaction L→Al+Si+β-Al₅Fe Si,respectively.The aging treatment of the alloy was carried out after high-pressure solidification.There have silicon enriched areas in theα-Al matrix,and these areas could provide nucleation masses for the precipitation of silicon phase.The interface between the precipitated phase and the matrix evolved gradually from semi-coherent relationship to incoherent relationship during the aging treatment.The nano-hardness and thermal conductivity of the alloy increased significantly during the aging treatment from 0 h to 12 h.The alloy exhibited typical age-hardening effects and a significant increase of theα-Al lattice constant.The alloy nano-hardness andα-Al lattice constant were not significantly changed during the aging treatment from 12 h to 24 h,while the thermal conductivity of the 3 GPa alloy decreased,indicating that the lattice distortion was not released after aging for more than 12 h,which had a limited effect on the improvement of thermal conductivity.The large number of precipitated phases in the 3 GPa solidification alloy was the main factor in the reduction of its thermal conductivity due to the incoherent interface between the precipitated phase and the matrix.