Exaggerated grain growth and surface marking in the forming of 6061 alloy sheet

Abstract

In the drop- or stretch-forming of operationa of frames of airplane parts which consisted of the heattreatable 6061 alloy sheet, unacceptable products were made many times extraordigrain growth or orange peel in materials.
Sheets of six different thickness from three different manufactures were picked up and examined their tendency of grain growth and studied on the correlation between the forming process and the grain growth.
It seems that the tendency of grain growth is different according to the manufacturer although the grain size (0.05mm) are almost same. The grain growth area has poor mechanical properties compared with the normal area. When the cold work is applied it must be restricted to 5% only before the solution treatment and can be made more after the treatment. The grain size becomes the maximum value when the cold work reaches 6∼7% (about 11kg/mm² load). When the grain size exceeds 0.1mm, the surface is completely covered with the orange peel effect.