The Study on Heat Treatment Microstructure and Properties of Extruded Al-Mg-Si-Mn-Cr-Zr Alloy

Abstract In order to obtain a high-strength Al-Mg-Si aluminum alloy with a tensile strength of more than 400MPa, a trace amount of Zr is added to the 6082 aluminum alloy to obtain an Al-1.0Mg-1.05Si-0.55Mn-0.15Cr-0.045Zr alloy. The mechanical properties and microstructure of the extruded Al-1.0Mg-1.05Si-0.55Mn-0.15Cr-0.045Zr alloy were studied by tensile performance test, metallography, scanning electron microscope (SEM), transmission electron microscope (TEM), electron backscatter diffraction (EBSD) observation and energy spectrum analysis. The results show that, after 545°C×2h+170°C×8h heat treatment, the alloy has the best mechanical properties. The tensile strength, yield strength and elongation at break reached 423MPa, 402MPa and 14%, respectively. The alloy strengthening mechanism is mainly due to the large number of dispersed needle-like β′ phases, sub-micron α-Al(MnCrFe)Si phases, α-Al(MnFe)Si phases and micron-level α-Al(MnCrFe)Si phases precipitated inside the grains and grain boundaries. The alloy precipitates sub-micron α-Al(MnCrFe)Si phase, α-Al(MnFe)Si phase and micron-level α-Al(MnCrFe)Si phase. After the alloy is treated at 545°C×2h+170°C×8h, a large number of dispersed needle-like β″ precipitations are uniformly precipitated in the inside the grains respectively. These precipitations can improve the strength of the material. The average grain size of the alloy is 7.41μm, and a bimodal grain structure composed of low-angle grain boundaries and high-angle grain boundaries is formed.