The Influence of Cu on the Aging Mechanical Properties and Precipitate Behavior of Si-Rich Al-Mg-Si Alloy

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The influence of Cu addition on the age-hardening response, mechanical properties, and precipitation evolution of Si-rich Al–Mg–Si alloy was investigated by hardness test, room-temperature tensile test, and transmission electron microscopy analysis. The results indicate that the addition of Cu significantly enhances the aging–hardening response of the alloy, promotes the hardness and room-temperature tensile strength under the peak-aged state, and reduces the softening rate during over-aging. The peak-aged tensile strength of the Cu-added alloy (387 MPa) was approximately 9% higher than that of the Cu-free alloy (355 MPa), and the elongation to failure of the Cu-added alloy reached 19%, significantly exceeding the 15% exhibited by the Cu-free alloy. The Cu promotes the precipitation of under-aged and peak-aged β″ strengthening phases within the alloy grains, while also facilitating the formation of lath-shaped Q’ and L phases in peak-aged and over-aged microstructures. This enhances the room-temperature tensile properties of the alloy in the peak-aged state and reduces the attenuation of over-aged properties. Furthermore, Cu influences grain boundary precipitation behavior by promoting the formation of Cu-rich precipitates along grain boundaries and reducing the width of precipitation-free zones (PFZs).