Thermal Annealing Effect on Elastic-Plastic Behavior of Al-Si-Cu Structural Films Under Uniaxial and Biaxial Tension

In this paper, the influence of thermal annealing on the elastic-plastic behavior of Al-Si-Cu films under uniaxial and biaxial tensile stress states is described. For the mechanical evaluation of the films, we used an in-plane biaxial tensile test equipment that was specially designed and developed. In the uniaxial tensile test in which the strain rate was varied from 4.0×10^-4 to 5.0×10^-3 s^-1, annealing at 623 K (350 ^°C) in N₂ gas for 1 h did not affect the Young´s modulus. The mean value was found to be 64.5±5.6 GPa. The yield strength showed annealing dependency. The mean yield strength was 168.5±2.2 GPa and 128.1 ± 9.7 GPa for as-deposited and annealed films, respectively. In the biaxial tensile test in which the strain rate ratio was changed between 1:1 and 1:5 in Cartesian coordinates, tensile force and displacement were well controlled. The stresses at the time of yielding were fitted well using the yield equation of Hill with different Lankford coefficient values. X-ray diffraction and electron backscatter diffraction (EBSD) analyses demonstrated that the films had a <;111> fiber texture. The grain growth and sharpening of the texture with annealing were observed in the EBSD analysis. Auger electron spectroscopy analysis suggested that a reduction in yield strength after annealing was related to Cu segregation at the grain boundaries, in addition to grain growth during annealing.