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 90A degrees, and controlling the rotation of the billets between sequential passes.