This is a skin delamination defect formed when the metal flow is relatively uniform, and the surface of the ingot flows into the product along with the interface between the mold and the front end elastic zone. On the horizontal low magnification test piece of industrial aluminium profile, there are defects of different layers at the edge of the section.
1. The main cause of stratification
(1) There is dust on the surface of the ingot or the ingot has large segregation aggregates instead of car skin, metal tumors, etc., which are easy to form layers;
(2) There are burrs on the surface of the blank or dirt such as oil stains, sawdust, etc., which are not cleaned before extrusion;
(3) The position of the die hole is unreasonable, close to the edge of the extrusion cylinder;
(4) The extrusion tool is severely worn or there is dirt in the bushing of the extrusion cylinder, which cannot be cleaned and replaced in time;
(5) The diameter difference of the extrusion pad is too large;
(6) The temperature of the extrusion cylinder is much higher than that of the ingot.
2. Prevention methods
(1) Reasonable design of molds, timely inspection, and replacement of unqualified tools;
(2) Unqualified ingots are not installed in the furnace;
(3) After cutting the residual material, it should be cleaned up without sticking to the lubricating oil;
(4) Keep the lining of the extrusion cylinder intact, or clean the lining in time with a gasket.
The phenomenon of weld delamination or incomplete welding of the hollow product extruded by the split die at the weld is called poor welding.
1. The main cause of poor welding
(1) The extrusion coefficient is small, the extrusion temperature is low, and the extrusion speed is fast;
(2) Extrusion wool or tools are not clean;
(3) Oiling the aluminium extruded profiles;
(4) Improper mold design, insufficient or unbalanced hydrostatic pressure, unreasonable design of shunt holes;
(5) There is an oil stain on the surface of the ingot.
2. Prevention and control methods
(1) Properly increase the extrusion coefficient, extrusion temperature, and extrusion speed;
(2) Reasonable design and manufacture of molds;
(3) The extrusion cylinder and extrusion gasket are not oiled and kept clean;
(4) Use ingots with clean surfaces.
This is a small arc-shaped crack at the edge of the transverse test piece of the extruded product and periodic cracking at a certain angle along its longitudinal direction. In mild cases, it is hidden under the epidermis, and in severe cases, the outer layer forms zigzag cracks. Industrial aluminium profiles can severely disrupt metal continuity. Extrusion cracks are formed when the metal surface is torn apart by the excessive periodic tensile stress of the die wall during the extrusion process.
1. The main cause of extrusion cracks
(1) The extrusion speed is too fast;
(2) Extrusion temperature is too high;
(3) The extrusion speed fluctuates too much;
(4) The temperature of the aluminium extrusion wool is too high;
(5) When the porous die is extruded, the die arrangement is too close to the center, so that the central metal supply is insufficient so that the difference between the center and the edge flow rate is too large;
(6) The ingot homogenization annealing is not good.
2. Prevention and control methods
(1) Strictly implement various heating and extrusion specifications;
(2) Frequent inspection of instruments and equipment to ensure normal operation;
(3) Modify the mold design and carefully process it, especially the design of the mold bridge, welding room and edge radius, etc. should be reasonable;
(4) Minimize sodium content in high magnesium aluminium alloys;
(5) The ingot is homogenized and annealed to improve its plasticity and uniformity.