Avoiding cracks and inhomogeneities in billets processed by ECAP

Although equal-channel angular pressing (ECAP) is now an established technique for producing bulk ultrafine-grained metallic materials, processing difficulties may arise because of the occurrence of cracking or inhomogeneities. This problem is examined with reference to experimental data for aluminum and magnesium alloys and a Pb–Sb alloy. It is shown that effective procedures are available for avoiding the development of inhomogeneities and the cracking of billets during ECAP: these procedures include introducing a pre-deformation of the as-cast material prior to ECAP, decreasing the strain produced in each ECAP pass by using dies with angles higher than 90°, and controlling the rotation of the billets between sequential passes.