Comparison of flow behavior of as-cast and hot rolled Al-B4C composites by constant and differential strain rate tests

High temperature tensile flow behavior of aluminum-boron carbide (Al-B4C) composites of 0, 5 and 15% B4C, hot rolled to similar to 88% with intermediate annealing at 350 degrees C, was investigated by constant initial strain rate (CIS) ((epsilon) over dot = 1 x 10(-2)s(-1)) test technique at 500 degrees C and strain rate jump ((epsilon) over dot = 5 x 10(-5) - 1 x 10(-2)s(-1)) test technique over the temperature range of 400-500 degrees C. In the as-cast condition, the flow stresses obtained between CIS and strain rate jump test techniques were found to be significantly different at 500 degrees C. The strain rate sensitivity index (m) was found to be similar to 0.1 over (epsilon) over dot = 1 x 10(-4) - 1 x 10(-2)s(-1) for all the composites in both as-cast as well as hot rolled condition. Tensile elongations were found to be 0.36 in both as-cast and hot rolled aluminum, whereas the same reduced in Al-5% B4C composite to 0.35 and 0.27, respectively. The values of activation energy (Q) for deformation of rolled aluminum and Al-5% B4C composite were determined to be 194.2 and 73.4 kJ/mol, respectively. The microstructural examination, using SEM and EBSD techniques, revealed cavitation in aluminum upon differential strain rate test, and grain refinement upon rolling, which increased later during tensile test.