Papers by Keyword: Atom Probe Analysis

Abstract: Hardness measurements and 3-dimensional atom probe analysis have been used to characterise the precipitation behaviour in two 6xxx series aluminium alloys, one Cu-free alloy (Al-0.78at%Mg- 0.68at%Si) and one Cu-containing alloy (Al-0.78at%Mg-0.68at%Si-0.30at%Cu). The heat treatments consisted of either natural ageing or pre-ageing at 353K followed by a paint-bake treatment at 453K. Natural ageing was seen to increase the hardness, and hence reduce formability compared to pre-ageing. In addition, the strengthening effect of artificial ageing was less after natural ageing than after pre-ageing. In the Cu-free alloy, needle-like β″ was observed to form only after a pre-ageing treatment during the first 60 minutes of a paint-bake treatment. In the Cucontaining alloy, needle-like β″ formed during paint bake in both the naturally-aged and pre-aged material, although it is formed more rapidly after pre-ageing. This was accompanied by an increase in strength over the Cu-free alloy and indicates that Cu reduces the deleterious effect of natural ageing.

Abstract: The formation of nano-scale clusters (nanoclusters) prior to the precipitation of the strengthening b” phase significantly influences two-step aging behavior of Al-Mg-Si alloys. In this work, the existence of two kinds of nanoclusters has been verified in the early stage of phase decomposition by differential scanning calorimetry (DSC) and three-dimensional atom probe (3DAP). Pre-aging treatment at 373K before natural aging was also found to form preferentially one of the two nanoclusters, resulting in the remarkable restoration of age-hardenability at paint-bake temperatures. Such microstructural control by means of optimized heat-treatments; i.e. nanocluster assist processing (NCAP), possesses great potential for enabling Al-Mg-Si alloys to be used more widely as a body-sheet material of automobiles.

Abstract: The nano-scale precipitate microstructures and properties of age-hardenable aluminum alloys such as Al-Cu, Al-Mg-Si and Al-Zn-Mg alloys were investigated using conventional electrical resistivity and hardness measurements, TEM and 3D-AP techniques. To increase mechanical strength and ductility of the alloys nano-scale precipitates were effectively controlled by applying new type heat treatments and microalloying elements. In the initial stage of phase decomposition of the alloys containing microalloying elements several types of nanoclusters were formed and distinctly detected by the 3D-AP technique. These nanoclusters greatly affect the nucleation of the subsequent precipitates and resultantly mechanical properties. In Al-Mg-Si and Al-Zn-Mg alloys complicated two-step aging behaviors were found to be originated in the positive or negative effect of the nanoclusters with different structures.