Solidification characteristics of the Al-8.3Fe-0.8V-0.9Si alloy

Studies of solidification behavior have been conducted on cast Al-Fe-V-Si alloys. The first phase to precipitate during solidification of an Al-8.3Fe-0.8V-0.9Si alloy is Al3Fe(V,Si), which is isostructural with the Al3Fe phase. Thereafter, the solidification proceeds through several invariant reactions. The final invariant reaction is associated with a pronounced arrest. The temperature of this arrest is a function of the cooling rate and modification treatment, with magnesium added as an Al-20 pct Mg or Ni-20 pct Mg master alloy. The coarse iron aluminide precipitates in a slow-cooled (>1 °C/s) cast structure transform to a ten-armed, star-like morphology upon chill casting the melt (cooling rate >10 °C/s) from 900 °C or upon water quenching from above 800 °C. Treatment with magnesium refines the morphology, size, and distribution of iron aluminide precipitates in slow-cooled alloys

Role of Al2O3 particulate reinforcements on precipitation in 2014 Al-matrix composites

This publication is a work of the U.S. Government as defined in Title 17, United States Code, Section 101. Copyright protection is not available for this work in the United States.Precipitation in commercial aluminum alloy 2014, without and with alumina particulate reinforcements, was studied using microhardness, electrical resistivity, differential scanning calorimetry (DSC), and transmission electron microscopy. The precipitation sequence in 2014 Al was confirmed to be [alpha][sub ss] [yields] [alpha] + GPZ [yields] [alpha] + [lambda][prime] [yields] [alpha] + [lambda][prime] + [theta][prime] [yields] [alpha] + [lambda] (AlCuMgSi) + [theta] (CuAl[sub 2]). Reinforcement addition decreased the time to peak hardness, but also reduced the peak matrix microhardness. This was traced to a decrease in the amount of [lambda][prime] formed in the composites. Further, it was observed that while Guinier-Preston (GP) zone and [theta][prime] formations are accelerated in the composites, [lambda][prime] precipitation is decelerated. The acceleration is attributable primarily to enhanced nucleations resulting from an increase in the matrix dislocation density due to coefficient of thermal expansion (CTE) mismatch between the matrix and the reinforcements, whereas the deceleration is associated with a decrease of low-temperature solute diffusivity due to absorption of vacancies at dislocations and interfaces. It was also observed that the degree of overall acceleration in hardening and the reduction in peak matrix microhardness with reinforcement addition decreased with decreasing aging temperatures. The causal relationships of these observations with the associated mechanisms are discussed.Non