Characterisation of Precipitation Hardening Response and As-Quenched Microstructures in Al-Mg(-Ag) Alloys

Abstract

The age-hardening response in Al-Mg alloys, with and without trace additions of Ag, aged isothermally at 160 C, 200 C and 240 C was investigated. Additionally, the effects on ageing response of cold work introduced after solution treatment, water quenching and prior to the ageing treatments were clarified for the Al-Mg-(Ag) alloy. The dislocation populations in the as-quenched microstructures of Al-10 mass% Mg alloys with and without trace additions of Ag were characterised. Trace additions (0.5 mass%) of Ag to Al-Mg alloys with low solute Mg contents (<5 mass%) promote an age-hardening response, while similar additions to Al-Mg alloys with higher solute Mg contents (e.g. 10 mass%) enhance significantly the age-hardening response. The age-hardening response in an Al-10Mg-0.5Ag (mass%) alloy is significantly enhanced by the introduction of 7% cold work, post solution treatment and prior to ageing at 160 C and 200 C. The identity of the dislocations in as-quenched Ag-free and Ag-modified Al-10 mass% Mg alloys has been confirmed as unit perfect a=2h110i type. The addition of Ag does not appear to modify the form of the dislocations and no dissociation of these dislocations was observed. The density of dislocations in the solution treated and quenched condition in the Al-10 mass% Mg alloy was higher by a factor of $2 compared to that in the Al-10Mg-0.5Ag (mass%) alloy subjected to similar treatment.

Formation of Quasicrystalline Particles in an Isothermally Aged Al-10 Mg-0.5 Ag (mass%) Alloy

“…3 would suggested that the sharpness and sphericity of the electron diffraction spots in all three zone-axis diffraction patterns, combined with the observation that all main diffraction spots are perfectly aligned and angles between major row of reflections are as required for the icosahedral symmetry of zone axis, are an indication that the alloy is not a collection of multiple-twinned nanoscale crystallites. 23) It is interesting to note that the newly found quasicrystalline metastable precipitate particles appear to be the primary strength phase in the Al-10 Mg-0.5 Ag (mass%) alloy aged at 240 C. [24][25][26] This result is a quite important to design the microstructures for automobile and aerospace applications. The quasicrystalline particles transform into the crystalline T phase after aged during the period from 50 min.…”

Atomistic details of precipitates in lean Al–Mg–Si alloys with trace additions of Ag and Ge studied by HAADF-STEM and DFT

“…We have therefore decided to look more closely into adding Ag and Ge to a lean, industrially relevant Al 6xxx alloy, relating calculated parameters like solute misfit volumes and vacancy bonding energies to experimental observations. It has recently been found that, if a small amount of Ag is added to an Al-Mg-Si alloy GPzone formation is enhanced, which correlates with an increased peak hardness of the material [4]. HAADF images showed that Ag occupies Al sites in the matrix as well as in the precipitate, but preferably in the immediate vicinity of the interface [9].…”

“…The needles in 6xxx alloys mainly consist of Mg and Si in addition to Al itself [1] [2] [3], but other added elements may enter the precipitates as well. Elements like Li, Cu, Zn, Ag and Ge have proven to be beneficial for the nucleation and growth of precipitates, and they have consequently been added in multiple combinations and amounts [4] [5] [6] [7] [8]. It is beneficial for the extrusion and rolling processes to keep the alloys as lean as possible.…”

Effect of Trace Additions of Ag on Precipitation in Al&ndash;Mg Alloys

“…Discussion 4.1 Precipitation hardening response and precipitation sequence It has been reported that the age-hardening response of the Al-10Mg alloy is dramatically enhanced by trace additions of Ag. 24) In this case, the addition of Ag both accelerates the hardening response and leads to a significant increase in maximum hardness at a given ageing temperature. One potential source of this stimulation of the age-hardening response and this improved hardening behaviour in the Al10Mg-0.5Ag alloy derives from observations 11,12) that as little as 0.5 Ag reduces substantially the solubility of magnesium in aluminium over the full range of temperatures below the eutectic temperature.…”