The Effect of Silver Content on the Precipitation of the Al-4.6Cu-0.3Mg Alloy

Abstract

The effect of Ag concentrations of up to 0.9 mass% on the precipitation of the strengthening phases in Al-4.6Cu-0.3Mg casting alloy were investigated. Microstructural features were elucidated by optical microscopy, electron probe X-ray microanalysis, measurement of electrical conductivity and differential scanning calorimetry. The microstructure was correlated with Rockwell hardness. The results revealed that the addition of Ag at a concentration of under 0.6 mass% promoted the precipitation of the and 0 phases and the augmentation of hardness of T7 tempered alloys. 0.9 mass% Ag caused the extensive precipitation of the phase, but only mildly suppressed the precipitation of the 0 phase, slightly increasing the hardness. The high density of the precipitates of the phase is responsible for the excellent thermal stability and mechanical properties of the microstructure. The precipitates out before the 0 phase, and does so more quickly, during the aging process.

Impact of Cu/Mg Ratio on Thermal Stability of Hot Extrusion of Al-4.6 Pct Cu-Mg-Ag Alloys

“…The hardness of the T7-tempered cast A201 alloy, with a chemical composition that approached that of alloy B, was around HRB 73. [35] It was slightly lower than the T7-tempered hot-extruded alloy B. The hotextruded alloy should exhibit much better mechanical properties than the casting alloy, which in fact may be attributed to the suppression of the h¢ phase by the hotextrusion process, which eliminated the nuclear site of h¢ phase.…”

“…The DSC profiles obtained following solid solution treatment, shown in Figure 3, display exothermic precipitation peaks of the X, h¢, and S phases, which were partially overlapped. [33][34][35] The exothermic precipitation peaks of the X phase were near 223°C, 228°C, and 235°C for alloys A, B, and C, respectively. The exothermic precipitation peak of the h¢ phase appeared at around 320°C for alloy A and 270°C for both alloys B and C. The intensity of the exothermic precipitation peak of the S phase was weak and presented at about 358°C, 296°C, and 261°C for alloys A, B, and C, respectively.…”

“…The heats of precipitation of the X phase under the as-quenched condition were 0.45, 1.43, and 2.01 J/g for alloys A, B, and C, respectively, revealing that the alloy with the low Cu/Mg ratio alloy was present in greater quantities than that with the high Cu/Mg ratio. The alloy with the high Mg concentration induces dense Ag-Mg and Mg co-clustering, with the clusters acting as nucleation sites [35] for the X phase. Therefore, the alloy with the low Cu/Mg ratio contains a large amount of the X phase.…”

“…Due to the overlapping of X, h¢, and S exothermic precipitation peaks, the numerical simulation method [35] was employed to characterize these overlapping peaks, and the results were shown in Table III. The heats of precipitation of the X phase under the as-quenched condition were 0.45, 1.43, and 2.01 J/g for alloys A, B, and C, respectively, revealing that the alloy with the low Cu/Mg ratio alloy was present in greater quantities than that with the high Cu/Mg ratio.…”

Influence of welding parameters and post-weld aging on tensile properties and fracture location of AA2139-T351 friction-stir-welded joints

“…Mg is known to be crucial for the formation of the W phase in Al-Cu alloys, and Ag accelerates its precipitation. Indeed, the strong interaction between Ag and Mg results in the generation of Mg-Ag clusters which act as sites for the nucleation of W. Moreover, W is more stable than q' at the usual aging temperatures (≤ 200 °C), indicating that the 2139 exhibits excellent mechanical strength up to 200 °C 19,20 . In T351 condition, the 2139 is hardened by the Cu GP-zone formation, as demonstrated 21 .…”