Papers by Author: Michel Suéry

Abstract: This paper is concerned with the tensile behavior of various Al alloys during solidification obtained by using an initially solid specimen heated locally until it becomes fully liquid and then partially solidified at a controlled cooling rate. It is shown that for Al-Cu as well as for Al-Si-Mg alloys, a similar behavior is observed with a sharp transition on the stress-solid fraction curve when the coalescence solid fraction of the dendrites is reached. Below the transition fracture occurs along liquid films for very low stresses whereas beyond this transition, ductile fracture is observed leading to higher stresses.

Abstract: X-ray micro-tomography has been applied recently in a wide range of research fields (damage in materials, solidification …). Thanks to the high flux of synchrotrons and specific cameras the total time to acquire a scan was considerably reduced. The use of a specific camera based on CMOS technology allows dividing the acquisition time for a complete scan by a factor of 100. Therefore we have been able to perform in situ solidification of aluminium-copper alloys at high cooling rates (between 1 and 10°C/s) and we will show results concerning the evolution of the microstructure in 3D in the early stage of solidification, in particular the morphology of the solid phase and the kinetics of growth.

Abstract: The shear behavior of aluminum alloys containing increased amounts of Si or Mg compared with the 6061 alloy has been investigated by carrying out isothermal and non-isothermal tests in the mushy state during solidification. In isothermal conditions, it is shown that (i) an increase in Mg content leads to a more resistant semi-solid alloy compared with the 6061 alloy for the same solid fraction and (ii) an increase in Si content leads to a more brittle mushy alloy. In non-isothermal conditions, stress increases continuously with decreasing temperature with the formation of cracks for some compositions. This study shows that an increase in Mg content seems to be the most appropriate solution to reduce the formation of cracks in a solidifying 6061 alloy.