Microstructure characterization and hardness of Al-Cu-Mn eutectic alloy

The composition of Al-Cu-Mn ternary eutectic alloy was chosen to be Al-32.5wt.%Cu-0.6wt.%Mn to the Al2Cu and Al12CuMn2 solid phases within an aluminum matrix (α-Al) from its melt. The Al-32.5wt.%Cu-0.6wt.%Mn alloy was directionally solidified at a constant temperature gradient (G=8.1 K·mm-1) with different growth rates, 8.4 to 166.2 μm·s-1, by using a Bridgman-type furnace. The eutectic temperature (the melting point) of 547.85 °C for the Al-32.5wt.%Cu-0.6wt.%Mn alloy was obtained from the DTA curve of the temperature difference between the test sample and the inert reference sample versus temperature or time. The lamellar spacings (λ) were measured from transverse sections of the samples. The dependencies of lamellar spacings (λAl-Al2Cu) and microhardness on growth rates were obtained as, λAl-Al2Cu=3.02V-0.36, HV=153.2(V)0.035, HV=170.6(λ)-0.09 and HV=144.3+0.82(λAl-Al2Cu)-0.50, HV=149.9+53.48V0.25, respectively, for the Al-Cu-Mn eutectic alloy. The bulk growth rates were determined as λAl-Al2Cu2·V = 25.38 μm3·s-1 by using the measured values of λAl-Al2Cu and V. A comparison of present results was also made with the previous similar experimental results.