Causes of Welds in Aluminum Alloy Hollow Profiles

[China Aluminum Network] hollow profile is a common aluminum alloy decorative materials and industrial profiles, but also the aluminum factory often produces varieties, due to the different capacity of the extruder, may produce different hollow profiles in different models, such as Manufacture of 25mm×38mm flat tubes on 5MN machines, 100mm×25mm tubes on 8MN machines and curtain wall profiles, textile profiles or other industrial profiles on machines with 18MN or more. However, the problems often encountered in the production process are: Due to the serious weld seams, the black strips or the color difference after the surface treatment of the profiles cause the products to be scrapped, resulting in irretrievable losses. This article analyzes and summarizes relevant factors for reference by peers.

1. The formation mechanism of the weld metal is divided into several strands through the split hole and reassembled in the weldment chamber. Due to the existence of the diverter bridge, the rigid bottom of the metal flow is inevitably formed at the bottom of the bridge, and the metal atoms diffused and combined at a slow speed. Metallic Tissue density decreased. Therefore, the use of split-flow composite die extrusion will inevitably exist; but a good weld can make the profile after surface treatment to avoid such phenomena as black belt. To ensure the quality of the weld, the metal in the weld of the weld chamber must be fully diffused and bonded. Otherwise, loose, coarse particles and other parts of the structure will be uneven. Therefore, the degree of deformation must be larger, especially the welding room The amount of metal deformation is large to form a large hydrostatic pressure.

2. Causes of serious quilting 2.1 If the pressing force is too low, the welding force is low. The factors causing the low extrusion force are comprehensive, and there are some factors on the mold as well as the process. There are the following situations: First, the extrusion is relatively low. To increase the welding force, the following methods can be used: 1/ Upper die thickening 2/Shunt hole appropriately reduced 3/Extrusion temperature properly reduced, normal hollow profile extrusion temperature is 460-500°C, can be reduced to 420-440°C . This method is very practical at the scene.

4/ Select a larger extrusion tube, that is, arrange the extrusion on a larger model.

5/ The choice of welding room is deeper (can be done by "sinking" the shunt bridge). However, it should be noted that the sink bridge will also reduce the squeeze force, so the use of this method depends on the specific circumstances. For the use of "+ Yu" bridge structure of the shunt mode is more effective.

In fact, in the production process, with the wear of the mold, the wall thickness of the profile also increases, and the extrusion ratio also decreases. To a certain extent, the seriousness of the weld will affect the surface quality of the profile.

The design of the orifice is too large (especially for profiles with low extrusion ratio), which reduces the pressing force and thus reduces the welding force. It is recommended that the edge of the orifice be at least 6-10 mm from the wall of the squeeze tube. Of course, the choice of the split hole and the structure of the splitter bridge will be considered together better.

2.2 The welding chamber is too shallow or the volume is too small to form enough hydrostatic pressure. It is reasonable to increase the volume of the welding chamber under the premise of ensuring the rigidity and strength of the core. It may be to increase the cross-sectional area of ​​the welding chamber, or to increase the height of the welding chamber.

2.3 The layout of the shunt hole is irrational, and the design and processing of the shunt bridge are unreasonable. The weld should be made as far as possible to the corner or non-decorative surface, and the drip-type diverting bridge and reasonable welding angle should be adopted so that the welding point falls on the plane of the welding chamber (that is, the preforming area); if “+ The "bridge" structure is arranged with a split hole. Similar to this, the intermediate bridge can be narrower and the bridge (depth of the local weld depth) can be 5-8mm.

2.4 extrusion temperature is too high. (See Process Analysis) 2.5 Process 1/Aluminum Rod Quality and Composition The internal defects of the cast rod are likely to appear on the weld of the hollow profile (hard-to-deform zone). Excessive amounts of Mg and Si and excessively high Fe content will aggravate welding defects. It is recommended that the total amount of Mg and Si be in the range of 0.7% to 0.9%, and the Fe content of less than 0.15% can be better. Weld quality.

2/Extrusion temperature and extrusion speed The high temperature of the aluminum rod is conducive to the diffusion bonding of the metal, but it also leads to the intensification of the metal bonding die phenomenon. At the same time, the high temperature causes the metal's microstructure to grow and grow faster. , which will make the weld microstructure thick. The extrusion speed is too high, the metal deformation work increases, and the metal temperature rises more. In addition, the extrusion temperature is too high, the pressing force will be reduced, which in turn reduces the welding force. Therefore, at the production site, it is more practical to lower the temperature of the aluminum rod, and then perform the mold analysis and other analysis or maintenance.

3/Unreasonable choice of extrusion tube temperature will also affect the quality of the weld. For thick-walled profiles, the extrusion tube temperature is recommended to be 440-460°C. For thin-walled profiles and excessively large orifices, 400- At 420°C, on the other hand, the barrel is not clean, the excess amount of oxide scale is large, or the barrel has been deformed like a drum, and the gap between the barrel and the press pad is too large, which affects the quality of the weld.

4/ uneven cooling will also affect the quality of the weld. In fact, when graphite products are used as a slip-out station, the profiles are prone to black bands after oxidation, especially on hot summer days. This is due to the fact that the graphite's properties increase the temperature of the profile locally, thereby accelerating the grain growth at the surface weld. However, if the cooling capacity of the equipment is sufficient, this phenomenon can be avoided.

5/ To reduce the effect of the weld on the surface quality, it is also possible to relatively reduce the alkali corrosion time during the oxidation process.

3. Concluding Remarks To solve the problem of welding quality of hollow sections, it is necessary to first “diagnose” the mold, then select and ensure a reasonable process or adjust the extrusion process according to the conditions of the mold. The result of poor welding or severe welds is the appearance of ribbons such as black bands, chromatic aberrations, etc. after the profile has been surface treated.

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