The effects of Mg/Si ratios (0.86, 1.73 and 2.57) on the mechanical properties of aging Al–Mg–Si alloys containing Er and Zr micro-alloying elements were studied. The mechanical properties of the alloys were studied by Vickers micro-hardness (HV) measurements and tensile testing. Optical microscopy (OM) and transmission electron microscope (TEM) were used to observe the microstructures of the alloys. The results showed that different alloys with different Mg/Si ratios have four stages of age hardening. The alloy with a Mg/Si ratio of 1.73 possesses the highest hardness. In the peak-hardness aged condition (T6 state), the density of needle-like β″ phase increases first and then drops with the increase of Mg/Si ratio. When the Mg/Si ratio reaches 1.73, the highest density of needle-like β″ phase can be achieved. Er and Zr can improve the hardness of the alloys.
Mg/Si ratio Micro-alloying Age hardening behaviors Needle-like β″ phase
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