Development of a modified form of continuous equal channel angular processing (CECAP) of AA5xxx strain hardening Al-Mg alloys and a study of the resulting properties. Establishment of process parameters for in-line control

The work reported here was undertaken to seek a basis for in-line control of the gauge and surface quality of aluminium alloy sheet processed by continuous equal channel angular processing (CECAP) for strength and/or biaxial formability with particular reference to the machine developed in the authors’ laboratory. The mode of in-plane loading relative to the work zone (push vs push and pull) was found to be the most significant process variable in controlling output gauge. In general, feeding by push only tended to cause thickening of the sheet and the formation of a ridged surface associated with strong localisation of shear and concomitant poor surface, leading to shear failure in later passes. A combination of push and pull had the opposite effect, and a balanced combination provided the basis for maintaining output of constant gauge with a smooth surface. In the range of the investigation, gauge was a linear function of processing speed under a given set of in-plane and hold-down forces, decreasing linearly as speed of throughput increased, respectively, under push alone or push and pull, presumably as a result of changes in the friction forces. The very close correlation between gauge and strip speed under combined push and pull promises to provide a ready means of in-line control of output gauge and surface quality.