Corrosion behaviour and hardness of in situ consolidated nanostructured Al and Al-Cr alloys produced via high-energy ball milling

This paper presents a hypothesis and its experimental validation that simultaneous improvement in the hardness and corrosion resistance of aluminium can be achieved by the combination of suitable processing route and alloying additions. More specifically, the corrosion resistance and hardness of Al- xCr (x= 0-10 wt.%) alloys as produced via high-energy ball milling were significantly higher than pure Al and AA7075-T651. The improved properties of the Al- xCr alloys were attributed to the Cr addition and high-energy ball milling, which caused nanocrystalline structure, extended solubility of Cr in Al, and uniformly distributed fine intermetallic phases in the Al-Cr matrix.

Atom probe tomography investigation of heterogeneous short-range ordering in the 'komplex' phase state (K-state) of Fe-18Al (at.%)

We study an Fe-18Al (at.%) alloy after various thermal treatments at different times (24-336 h) and temperatures (250-1100 °C) to determine the nature of the so-called 'komplex' phase state (or "K-state"), which is common to other alloy systems having compositions at the boundaries of known order-disorder transitions and is characterised by heterogeneous short-range-ordering (SRO). This has been done by direct observation using atom probe tomography (APT), which reveals that nano-sized, ordered regions/particles do not exist. Also, by employing shell-based analysis of the three-dimensional atomic positions, we have determined chemically sensitive, generalised multicomponent short-range order (GM-SRO) parameters, which are compared with published pairwise SRO parameters derived from bulk, volume-averaged measurement techniques (e.g. X-ray and neutron scattering, Mössbauer spectroscopy) and combined ab-initio and Monte Carlo simulations. This analysis procedure has general relevance for other alloy systems where quantitative chemical-structure evaluation of local atomic environments is required to understand ordering and partial ordering phenomena that affect physical and mechanical properties.

Synthesis of Al-doped Mg2Si1-xSnx compound using magnesium alloy for thermoelectric application

Abstract Mg2Si1-xSnx thermoelectric compounds were synthesized through a solid-state reaction at 700 °C between chips of Mg2Sn-Mg eutectic alloy and silicon fine powders. The Al dopants were introduced by employing AZ31 magnesium alloy that contains aluminum. The as-synthesized Mg2Si1-xSnx powders were consolidated by spark plasma sintering at 650-700 °C. X-ray diffraction and scanning electron microscopy revealed that the Mg2Si1-xSnx bulk materials were comprised of Si-rich and Sn-rich phases. Due to the complex microstructures, the electrical conductivities of Mg2Si1-xSnx are lower than Mg2Si. As a result, the average power factor of Al0.05Mg2Si0.73Sn0.27 is about 1.5 × 10^-3 W/mK² from room temperature to 850 K, being less than 2.5 × 10^-3 W/mK² for Al0.05Mg2Si. However, the thermal conductivity of Mg2Si1-xSnx was reduced significantly as compared to Al0.05Mg2Si, which enabled the ZT of Al0.05Mg2Si0.73Sn0.27 to be superior to Al0.05Mg2Si. Lastly, the electric power generation from one leg of Al0.05Mg2Si and Al0.05Mg2Si0.73Sn0.27 were evaluated on a newly developed instrument, with the peak output power of 15-20 mW at 300 °C hot-side temperature.