Effect of Trace Additions of Ag on Precipitation in Al–Mg Alloys

Abstract

Effect of Ag additions on the precipitate microstructures of the Al-10Mg alloys has been investigated using transmission electron microscopy (TEM) and electron diffraction.In the Al-10Mg alloy aged at 240 C, age-hardening response is attributable initially to an array of coarse-scale, sparsely distributed rodlike and/or plate-like 0 precipitate (particles). At the maximum hardness, the microstructure contained an increased volume fraction of coarsescale 0 and precipitate particles. In a well over-aged condition, the microstructure exhibited very coarse-scale precipitate particles. However, in the Al-10Mg-0.5Ag alloy aged at 240 C, fine-scale and uniformly distributed icosahedral quasicrystalline precipitates were observed in the early stages of ageing, and it was to be replaced by the metastable crystalline T phase after the alloy is aged for 2 h at 240 C. The T phase formed as faceted rods parallel to h110i directions appeared to be the primary strengthening constitute exhibiting maximum hardness. The globular precipitate particles were observed to be replaced by the metastable rod-like T precipitate particles after the alloy was aged 72 h at 240 C, and the phase is confirmed to be the equilibrium constitute phase in the over-aged ternary Al-10Mg-0.5Ag alloy.

Observation of Beta Phase Particles in an Isothermally Aged Al-10 mass%Mg Alloy with and without 0.5 mass%Ag

“…0.5 h) 17) as well as the present microstructural observations for the Al-10 mass%Mg alloy aged at 200 C (e.g. 1, 2 and 4 h) in Figs.…”

“…2(a)) is indexed for a ½11 2 26 direction of a hexagonal structure, and suggests to be a metastable 0 phase. The previous paper revealed the formation of a precipitate cluster consisting of three distinguishable parts, such as blocky, irregularly-shaped and lath-like in the Al-10 mass%Mg alloy aged 5 h at 240 C. 17) These heat treatments again correspond to under-ageing conditions. 15) Another example from the microstructure of the binary alloy, aged 5 h at 240 C, is shown in Fig.…”

“…1, and this is consistent with the results previously reported. 17,19) This implies that nucleation of these particles appears to be energetically difficult. The nucleation of the phase (Al 3 Mg 2 ) has been studied by a number of researchers.…”

Evolution of Microstructure and Mechanical Properties of Novel Al-Mg-Mn-Ag-Cr-Zr Alloy

“…In recent years, some researchers have studied the aging process in Al-Mg-Ag alloys and found that the addition of Ag has a marked impact on the precipitation particles. The hardness of the alloy was improved conspicuously using only small amounts of Ag [15,16]. However, these researchers mainly focused on 5xxx series aluminum alloys, which contained over 10 wt.% Mg.…”

Influences of Ag Addition on the Microstructure and Mechanical Properties of Al-4Mg Alloy

“…In recent years, some research has reported that Ag played a positive role on aging hardening of an aluminum alloy [ 10 , 11 ]. For 5xxx aluminum alloys, the influence of Ag is mainly focused on the high-Mg content (>10 wt.%) Al-Mg alloys [ 12 , 13 ]. Due to the poor corrosion resistance and inferior processability, the application of high-Mg content Al-Mg alloys was limited.…”