Over burn

  When the industrial aluminum material is severely burned, the surface color is dark or black, or air bubbles, fine spherical precipitates (small bubbles), or cracks appear on the surface. In the metallurgical microstructure, grain boundary coarsening occurs. There is a triangle resolving zone at the grain boundary, and remelted spheres are produced inside the grain. The strength and elongation decrease in the mechanical properties.

  A cause

   The main cause of overheating is that the heating temperature is too high, beyond the allowable heating temperature range of the heat treatment process. Or the heating is not uniform, the temperature difference between the furnace is too large, the instrument fails, etc., so that the local aluminum profile reaches the melting temperature of the low-melting eutectic in local places, resulting in local overheating.

  B prevention method

  Overheating is mainly determined by Xin phase microscopy. It is inaccurate to use the mechanical property change inspection method because the mechanical properties change little for slight burns, sometimes even slightly, but it has a serious impact on corrosion resistance. Industrial aluminum burning is definitely a waste product. Strictly controlling the heating temperature is a guarantee of the heat treatment system that prevents over-burning. The maintenance of the equipment is strengthened to ensure that the temperature of the heating furnace does not exceed ±5°C. This is a guarantee for equipment that prevents over-burning.

 2. Coarse crystal ring

  A cause

  Industrial aluminum profile solution heat treatment, after low magnification inspection, found that the grain size on the cross-section is different, the cross-section surrounding grains are particularly thick, forming a ring or crescent-shaped organization, said coarse-grained ring, which makes the mechanical properties of industrial aluminum profiles reduce. The formation mechanism and influencing factors of the coarse-grained rings are relatively complex and no unified view has yet been formed. The reason may be that the extrusion deformation is not uniform, the outer layer metal is subject to mold wall friction, the physical deformation degree is large, and the dirt in the tail end material also gradually enters the outer layer. The surface layer of the heat treatment industrial aluminum profile has a higher heating temperature than the inner layer. For a long period of time, crystal nuclei are produced due to the inclusion of mixed impurities, which are likely to grow and cause the outer metal grains to become significantly coarser.

  B prevention method

  (1) The reverse extrusion method is used to deform the metal uniformly and it is not easy to form a coarse crystal ring.

  (2) Add a small amount of manganese, titanium, and iron to industrial aluminum profiles to reduce or eliminate coarse-grained rings.

  (3) According to the specific situation, the ingot does not undergo homogenization annealing.

  (4) Using high temperature extrusion to make the industrial aluminum profile in a single phase zone, which can reduce the depth of the coarse crystal ring.

  (5) Properly increase the size of the extrusion residue to avoid the flow of non-metallic inclusions in the residue into the end of the industrial aluminum profile.

   (6) Keep the inner wall of the squeeze tube clean and smooth to form a complete aluminum sleeve to reduce the friction during extrusion.

  (7) To avoid excessively high quenching temperature, reasonably formulate the heat treatment process system.

  (8) Using porous die extrusion.