Suppression of Serration of Al-Mg Sheet by Periodic Indentation

Al-Mg alloy sheets often show nonuniform deformation in sheet forming process. Surface defects, i.e., ridging/roping or stretcher’s strain, appear on the sheets. The surface defects decrease deformability of the sheets as well as surface quality of the products. It was reported that the nonuniform deformation is related to the dyamic strain aging or Portevin-LeChatelier effect. That is typically observed stress oscillation i.e., serration on stress-strain curve, in tensile tests. In order to suppress the serration, this study proposes periodic micro indentation on sheet surface to induce uniform deformation. The indentation was conducted on the four type of Al-Mg alloys with lattice-shaped pattern using an automatic hardness testor. The deformation becomes more uniform by the indentation, while tensile properties were not much influenced. It is found that the serration is suppressed with increasing density of indentations. It is also found that the serration is caused by strain oscillation and decreases with increasing Mg content.