[Chinalco.com] Chinalco shares with you the post-weld treatment of aluminum and aluminum alloys:
1. After removal of residual weldments After welding, if gas welding or coating welding is used, prior to appearance inspection and non-destructive testing of the welds, it is necessary to remove the residual fluxes and slags on the welds and both sides in time. Prevent weld slag and residual flux from corroding welds and their surfaces to avoid adverse consequences. Common post-weld cleaning methods are as follows:
(1) Brushing in hot water at 60°C~~80°C;
(2) Adding potassium dichromate (K2Cr2O2) or chromic anhydride (Cr2O2) with a mass fraction of 2% to 3%;
(3) Wash in hot water at 60°C~~80°C;
(4) Dry in the drying oven or air dry.
In order to test the effect of residual flux removal, distilled water can be dripped in the weld of the weldment. Distilled water is then collected and dropped into a small test tube with 5% nitric acid solution. If there is a white precipitate, it means that the residual remains. The flux has not been completely removed.
Second, the surface treatment of the weldment Through the appropriate welding process and the correct operating technology, the surface of the welded aluminum and aluminum alloy weld has a uniform, wavy and smooth appearance. Anodizing, especially when used in conjunction with polishing and dyeing techniques, results in a high quality decorative surface. To reduce the heat affected zone, anodization can be used to cause poor color changes to be reduced. Using the rapid welding process, the heat affected zone can be reduced to a greater extent. Therefore, flash butt welding seams have good anodizing quality.
Especially for the welded part of the alloy that cannot be heat-treated and strengthened in the annealed state, after the anodizing, the color contrast between the basic metal and the heat affected zone of the welding is small. Furnace and dip brazing are not locally heated, so the appearance of metallic color is very uniform. Heat-treatable alloys, often used as building structural parts, are often anodized after welding. In this kind of alloy, the welding heating will form the precipitation of alloying elements. After anodizing, there will be differences between the heat-affected zone and the weld. These halos around the weld zone can be reduced to a minimum using rapid welding, or the use of cooling pads and platens can also reduce the halos to a minimum. These halos are after welding and prior to anodizing. Solid handling can be eliminated.
In chemically treated weldments, the difference between the color of the weld metal and the base metal is sometimes encountered, which necessitates the careful selection of filler metal components. In particular, when the alloy composition contains silicon, it will have a color. The ratio has an effect.
If necessary, the weld can be mechanically polished. Commonly used mechanical polishing includes polishing, polishing, abrasive blasting, shot peening and the like. Mechanical polishing improves the surface of aluminum workpieces by physical methods such as grinding, deburring, rolling, polishing or sanding. Its purpose is to obtain the required surface quality through as few processes as possible. However, aluminum and aluminum alloys are soft metals, and the friction coefficient is relatively high. If overheating occurs during the grinding process, there is a possibility that the weldment may be deformed and fractured from the grain boundary. This requires sufficient lubrication during the polishing process and the pressure on the metal surface should be reduced to a low level.
Third, the post-weld heat treatment The purpose of post-weld heat treatment is to improve the structure and performance of welded joints or to eliminate residual stress.
The heat treatable aluminum alloy can be reheated after welding to restore the strength of the base metal heat affected zone to near the original strength. Under normal circumstances, joint damage is usually in the melting zone of the weld. After re-welding heat treatment, the strength of the weld metal, mainly depends on the scattered filler metal. When the composition of the filler metal and the base metal is different, the strength will depend on the dilution of the filler metal with the base metal. The better strength is compatible with the heat treatment used for the weld metal.
Due to the precipitation in the melting zone near the weld and the melting of grain boundaries, the toughness of some weldments of heat treatable aluminum alloys is poor, and if the conditions are not too severe, the post-weld heat treatment can redissolve the soluble components and result in more The uniform structure slightly improves the toughness and increases the strength greatly.
It is not practical to completely re-heat-treat the weldment. The weldment can be welded in solution heat treatment and artificially aged after welding. In this welding method, when a high welding rate is used, sometimes the performance can be significantly improved beyond that of the normal welding state. However, weldments rarely achieve full reheating performance.
Fourth, the weld of plastic and weld defects repair After a product is welded, the following shape defects weld must be reshaping:
(1) Large joints (that is, large stacks and widths are very unsightly);
(2) tumors. The tumors are too much molten metal, mechanically stacked together, not fused to the parent metal, not part of the weld, and must be removed;
(3) Intermittent welding arc welding. The orthopedic tool generally uses a spatula of various shapes so that the repaired appearance is basically the same as a good weld, and the base material cannot be scratched or cut when repaired.
According to national standards, repairs must be carried out for weld defects that are not allowed.
The procedure for rework is generally to determine the scope of rework, generally should be extended to the defects of 50 ~ 70mm. If the result of the flaw detection can be used to determine whether the defect is near the inside or outside of the product, the side can be repaired first. If it is not possible to determine which side belongs to, the double-sided repair must be performed. Generally, the outside is repaired first and then the inside is repaired. Defects must be excavated before repairing. If using a pneumatic chipping machine, the reinforcing height of the weld is first flattened with a flat spatula, and then the trench is used to open the ditch. The depth of the ditch is used to find the defect, and the defect is removed and exposed. In good condition metal. If the defect has a large defect and the groove is too wide or too deep, it must be repaired before it is fully repaired and then beveled again before formal rework soldering can be performed. Repair welds must be verified by inspection to meet the standard requirements, and it is better to pass the repair.