Small Additions Of Silver Research Articles

X-ray investigation of ageing in an aluminium-5% magnesium alloy with small silver additions

The structural changes associated with ageing of aluminium-5 wt.% magnesium alloys containing 0.5 and 1.0 wt.% silver have been investigated by X-ray diffraction methods. At lower temperatures and shorter times, the hardening is shown to be due to the formation of approximately spherical Mg-Ag zones having an AuCu I type structure. Initially the zones are coherent with the matrix but with further ageing their tetragonality increases, mainly due to a decrease in the c axis, and to accommodate the increasing stress, orientation changes occur such that (101)zone ∥(110) Al and [010]zone ∥[001] Al. The lattice parameters of the zones at this stage are a = 4.42 A ̊ , c = 3.48 A ̊ , c/a = 0.79 . Line breadth measurements indicate that they have an average size of at least 60 Å. At higher temperatures the hardening is due to the precipitation of a T phase, Mg 32(Al, Ag) 49 with (100) T ∥(112) Al and [001] T ∥ [11̄0] Al.

Evidence for a Ternary Phase in the Aluminium–Magnesium–Silver System

Polmear and Sargant1 and Polmear2 have recently reported that small silver additions will influence the age-hardening characteristics of aluminium–magnesium alloys. They show, for example1, that the precipitate in a wrought Al-7 wt. per cent Mg alloy is finer and more uniformly dispersed with resultant increase in hardening, on the addition of 0.5 wt. per cent silver, and they suggest that there may be an interaction between the magnesium and silver atoms.