Influences of Cu Content on the Microstructure and Strengthening Mechanisms of Al-Mg-Si-xCu Alloys

Abstract

The effects of the Cu content on the microstructure and strengthening mechanisms of the Al-Mg-Si-xCu alloys were systematically investigated using scanning electron microscopy (SEM), electron probe microanalysis (EPMA), transmission electron microscopy (TEM), and mechanical tensile tests. The results show that, the strengthening mechanisms change with the Cu content. For as-quenched alloys, solution strengthening (σSS) is predominant when the Cu content ≥2.5 wt.%, and of equivalent importance as grain size strengthening (σH-P) when the Cu content ≤1.0 wt.%. With respect to peak-aged alloys, precipitation strengthening (σppt) is predominant when the Cu content ≥2.5 wt.%, but σSS becomes predominant when the Cu content is 4.5 wt.%. As the Cu content increases from 0.5 to 4.5 wt.%, the main type of precipitates in alloy tends to change from a β″ phase to Q′ phase, and then to a θ′ phase. Among the three types of precipitates, θ′-precipitate causes the largest increase in yield strength (σ0.2) and the largest decrease rate in elongation. β″-precipitate leads to the smallest increase in σ0.2 and the smallest decrease rate in elongation. The increase of Cu content reduces Si solubility in the Al matrix and thus decreases the nucleation rate of β″ phase during subsequent aging.

Effect of the Solid Solution and Aging Treatment on the Mechanical Properties and Microstructure of a Novel Al-Mg-Si Alloy

“…An insufficient quenching rate after aging can minimize the strength of the alloy. When the rate of quenching decreases, there is a related decline in the activation energy of vacancy diffusion during the aging process, aging kinetics decreases, and the peak hardness after aging decreases [13][14][15]. This study conducted solid solution and aging treatment on hot extruded Al-Mg-Si alloys, and compared their mechanical properties.…”

Microstructure Evolution and Mechanical Properties of Al–Cu–Mg Alloys with Si Addition

“…It divides the diagram into two sections on the Al-rich corner: α-Al + Al 2 Cu (θ) + S and α-Al + Mg 32 (Al, Cu) 49 (T) + S. A quasi-binary eutectic reaction (L => α-Al + S) occurs at a Cu/Mg ratio of 2.40, resulting in various non-variant reactions in the Al-rich corner of Al–Cu–Mg ternary alloys [ 2 ]. Low-Mg-containing alloys in the α-Al + θ + S section of the diagram are primarily composed of a primary α-Al matrix and eutectic α-Al-θ phases, along with a small amount of eutectic α-Al-S phases [ 3 , 5 , 11 , 12 , 13 , 14 , 15 , 16 , 17 , 18 , 19 , 20 ]. High-Mg-containing Al–Cu–Mg commercial alloys have compositions lying in the α-Al + S + θ and α-Al + S sections of the diagram [ 1 , 2 , 19 , 20 , 21 ].…”

“…However, selecting a composition within the α-Al + S + T section of the Al–Mg–Cu ternary phase diagram results in the formation of T precipitates that can be dissolved during solution heat treatment, thus improving the precipitation hardening of high-Mg-containing alloys. In addition, the incorporation of minor quantities of other elements (such as Si, Ag, Mn, Zn, Ge, and Sn) has been reported to have a significant impact on the microstructure evolution and heat treatment response of Al–Cu–Mg alloys with low Mg content [ 11 , 12 , 13 , 14 , 15 , 16 , 17 , 18 , 19 , 21 ]. Despite extensive studies on Al–Cu–Mg alloys with low Mg content, there has been limited research on how alterations in chemical composition impact the microstructure evolution and heat treatment response of Al–Cu–Mg alloys that contain a high Mg content.…”

Microstructure Evolution and Solidification Behavior of a Novel Semi-Solid Alloy Slurry Prepared by Vibrating Contraction Inclined Plate

“…Alloying has an important effect on the microstructure and mechanical property of aluminum alloys [13]. For example, the appropriate addition of Mg and Cu elements helps improve the mechanical property of aluminum alloys [14,15]. The Sr element has a unique advantage of varying the morphology of eutectic Si phases [16,17].…”