Materials Science and Engineering, 75 (1985) 79-86 79 In Situ Tensile Testing of Solidifying Aluminium and AI-Mg Shells P. ACKERMANN and W. KURZ Swiss Federal Institute of Technology. Chemin de BeUerive 34, Ch-1007 Lausanne (Switzerland) W. HEINEMANN Concast Standard AG., T6distrasse 7, CH-8027 Ziirich (Switzerland) (Received May 30, 1984; in revised form January 17, 1985) ABSTRACT In this paper a new tensile test method which permits the in situ measurement of the mechanical properties of a solidifying shell is described. These properties are of great signi- ficance in casting and welding processes. In the apparatus developed, the tensile stress is applied in a direction which is perpendicular to the growth axis of the columnar crystals so that, when alloys are tested, the mechanical behaviour of the mushy zone can be studied, as well as its contribution to the mechanical strength of the shell. This information cannot be obtained from conventional tests made using a Gleeble-type machine because, for ex- ample, control of the orientation of the solidi- fication microstructure with respect to the tensile axis is too difficult. The present method was first calibrated by using pure aluminium, which had no associated mushy zone. The re- sults here compared favourably with those obtained from creep experiments. Then, Al- Mg alloys were considered and the results were analysed as a function of the extent and morphology of the mushy zone, as deduced from heat flow calculations. 1. INTRODUCTION During the process of solidification the shell of continuously cast strands is subjected to deformations which might lead to the for- mation of surface and internal cracks. This is especially true for the initial stages of the con- tinuous casting of steel, where the reciprocat- ing mould acts on the primary shell formed by the meniscus at the mould wall. Further- more, the partially solidified strand is subjected to mechanical and thermomechanical stresses while descending through the guiding and cooling systems. In order to ensure optimum machine design and the correct selection of process parameters, it is therefore essential to know the mechanical strength of the shell, its deformation behaviour and its susceptibility to hot cracking. Furthermore, this knowledge can be applied to static casting and welding where stresses are often induced by shrinkage. Published results of hot tensile tests and creep tests in which the mechanical strength of the solid near the melting point (T 0.99Tin where Tm is the melting point) was determined can be found, for example, for pure aluminium [1-3] and pure 5-Fe [4]. When' the strength of solidifying alloys is considered, complications arise because the section to be deformed consists of a completely solid shell as well as a solid plus liquid (mushy) zone which is extremely weak in tension. The ex- tent of this zone depends on the composition of the alloy and its thermal environment. In order to simulate this situation, samples have been melted, cooled to the desired tempera- ture and tested in situ [5, 6]. Rogberg [6] suggested that the mechanical behaviour of samples tested in this manner was different from that obtained by heating cast alloys from room temperature to the testing temper- ature. In these experiments, however, control of the solidification process and of the corre- sponding microstructure is difficult if not impossible. In the continuous casting of steel, it is im- portant to understand the strength and defor- mation behaviour of the columnar zone in a direction which is perpendicular to its growth axis. Therefore, an apparatus was built which permits the determination of the mechanical 0025-5416/85/$3.30 © Elsevier Sequoia/Printed in The Netherlands