Effect of the Type of Pre-Torsional Deformation on the Creep Rates of an Aluminium-Silicon-Zinc Alloy

Abstract

The effect of extraneous deformation on the c r e e p curves has been extensively investigated. It s e e m s that extraneous deformation, under certain conditions, results in a decrease in the c r e e p rates, which is due, in general, to the increase in the induced internal s t r e s s e s /1 to 5 , ' .The aim of the present work, in which the literature s e e m s lacking, is to compare the effect of the type of pre-torsional deformation given at room temperature on the tensile c r e e p rate. The torsional deformation is c a r r i e d out either unidirectionally or bidirectionally.The material used is an aluminium dilute alloy containing 0.25 wt% silicon and 0.26 wt% zinc, in the form of wire samples (1 mm in diameter and of length 100 mm) .The effect of pre-torsional deformation on the tensile c r e e p rate is investigated at 300 OC and under an applied tensile s t r e s s of 3 kp/mm2. The examined alloy samples are subjected to tensile c r e e p tests under three different conditions: a) samples annealed at 350 OC for 3 h, b) one s e t of the annealed samples are subjected (while in place) to unidirectional type of torsion and given five twists (N = +5) before the c r e e p test, c) another set of the annealed samples are subjected to bidirectional type of torsion before the c r e e p test. The samples are given five turns of twist in the forward clockwise direction followed by an equal number of twists in the anti-clockwise direction (N = -+5).in Fig. 1 . It can be seen that the c r e e p strain a t any instance of time of predeformed samples is relatively low compared with those of annealed samples.The results of observations of the c r e e p strain-time relation are illustrated 1) Dokki, Cairo, Egypt.