The approximate distribution of coarse grains on aluminum profiles is:
(1) The distribution of the aluminum extruded profile in the longitudinal direction is thick at the front end and thick at the back end, and has a tapered tubular shape. The coarse-grained area and the fine-grained area have obvious boundary lines. In severe cases, coarse-grained structures appear in the whole section. ;
(2) The aluminum alloy bar extruded by a single hole die is uniformly distributed in the periphery after quenching. The bar extruded from the porous die has a crescent shape in a portion of the periphery of the bar after quenching. The number of die holes is small, the crescent-shaped coarse crystal ring is long, and the number of die holes is large, and the crescent-shaped coarse crystal ring is short;
(3) When the hollow profile is extruded, it tends to appear on the surface around the hollow portion of the profile. The outer surface is more obvious; when the wall thickness is larger, the thickness of the coarse crystal ring is also larger;
(4) At the end of the aluminum extruded profile, a portion of the coarse crystal ring is often introduced into the center of the article.
Second, the main reasons: three cases
(1) The heating temperature is too high during the heat treatment;
(2) The holding time is too long, or the heating rate is too slow;
(3) The deformation of the cold deformed metal is too small or annealed at a critical deformation temperature.
3. Measures to prevent coarse grains:
(1) Reasonably selecting the heating temperature and holding time of the heat treatment;
(2) increase the heating rate;
(3) For metals that require cold deformation, the degree of heating deformation should be increased to avoid annealing at critical temperatures.