Extrusion effect on 61S aluminium alloy

Abstract

A study was made on the effects of extrusion conditions, heat-treating temperature and chromium content on the tensile strength of the extruded 61S. A extrusion effect was observed when billets were extruded at the temperature higher than 400°C, and then the tensile strength increased with the elevation of the billet temperature. The critical tempertaure of the billet which produces the extrusion effect is a function of chromium content, and the temperature becomes lower according with the increase in chromium content. The critical chromium content which srises the extrusion effect is about 0.3 percent, and the tensile strength is nearly constant regardless of the billet temperature when chromium is less than the critivcal content. The extrusion effect was observed markedly when the billets were extruded without soaking. Both the solution heat-treating temperature and the extrusion ratio affect on the extrusion effect. It is obvious that the above mentioned extraordinary strengthening characteristic is connected with some factors governing the recrystallization temperature of extruded 61S.We discussed the above results and suggested that the extrusion effect may be resulted from the overlap of two effect i. e. substructure hardening effect and the strengthening effect resulted from the interaction between the edge dislocations at subboundaries and the solute atoms in G. P. zones formed at subboundaries in low temperature aging, and that a press effect can be explained rather by the above mentioned mechanism than the strengthening effects depended on texture and anisotropoic hardening.