Post-weld heat treatment of aluminum and aluminum alloy

First, remove the residue

After the welding of the weldment, if the welding or welding of the welding rod is used, the weld and the residual flux and welding slag on both sides should be removed in time before the visual inspection and non-destructive testing of the weld to prevent the welding residue and Residual flux corrodes the weld and its surface to avoid adverse consequences. Common post-weld cleaning methods are as follows:

(1) brushing in hot water at 60 ° C ~ ~ 80 ° C;

(2) Putting potassium dichromate (K2Cr2O2) or chromic anhydride (Cr2O2) with a mass fraction of 2% to 3%;

(3) Washing again in hot water at 60 ° C ~ ~ 80 ° C;

(4) Put it in a dry box to dry or air dry.

In order to check the effect of residual flux removal, distilled water can be added to the weld of the weldment, and then the distilled water is collected and dropped into a small test tube containing 5% nitric acid solution. If there is a white precipitate, it means that it 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 welded aluminum and aluminum alloy weld surface has a uniform corrugated smooth appearance. Anodized, especially when combined with polishing and dyeing techniques, results in a high quality decorative surface. Reducing the heat affected zone of the weld can be achieved by using anodizing to minimize undesirable color changes. The use of a fast soldering process minimizes the heat affected zone of the weld. Therefore, the weld of the flash butt welding has good anodization quality.

Especially for the welded parts of the alloy which cannot be heat-treated in the annealed state, after the anodizing treatment, the color contrast between the metal basic and the welded heat affected zone is the smallest. Furnace and dip brazing are not locally heated, so the appearance of the metallic color is very uniform. Heat treatable reinforced alloys, often used as building structural parts, are often anodized after welding. In such alloys, soldering heating forms alloying elements, and after anodizing, there is a difference between the heat affected zone and the weld. These halos around the weld zone can be minimized using rapid welding, or the halo can be minimized by using cooling pads and pressure plates. These halos are solidified after welding and before anodizing. Fall processing can be eliminated.

In chemically treated welded parts, sometimes the difference between the weld metal and the base metal is large, which requires him to carefully select the composition of the filler metal, especially when the alloy contains silicon. The ratio has an effect.

The weld can be mechanically polished if necessary. Commonly used mechanical polishing includes polishing, polishing, abrasive spraying, shot peening, and the like. Mechanical polishing improves the surface of an aluminum workpiece by physical methods such as grinding, deburring, rolling, polishing or sanding. Its purpose is to achieve the required surface quality with as few processes as possible. However, aluminum and aluminum alloys are soft metals, and the friction coefficient is relatively high, and if overheating occurs during the grinding process, the weldment may be deformed and the base may be broken from the grain boundary. This requires adequate lubrication during the polishing process and the pressure on the metal surface should be minimized.

Third, post-weld heat treatment

The purpose of post-weld heat treatment is to improve the microstructure and properties of the welded joint or to eliminate residual stress.

After the heat-treated reinforced aluminum alloy is welded, heat treatment can be performed again to restore the strength of the heat-affected zone of the base metal to near the original strength. In general, the joint failure is usually in the melting zone of the weld. After re-weld heat treatment, the strength of the weld metal is mainly determined by the filler metal that is scattered. When the filler metal is different from the composition of the base metal, the strength will depend on the dilution of the filler metal to the base metal. The best strength is compatible with the heat treatment used to weld the metal.

Due to the precipitation of the melting zone near the weld and the melting of the grain boundaries, the toughness of some weldments of the heat treatable reinforced aluminum alloy is very poor. If the situation is not too serious, the post-weld heat treatment can re-dissolve the soluble components and obtain more The uniform structure slightly improves the toughness and increases the strength greatly.

It is not practical to perform a complete reheat treatment of the weldment. The weldment can be welded in a solution heat treatment state and subjected to artificial aging treatment after welding. In this welding method, when a high welding rate is used, sometimes the performance can be remarkably improved beyond the strength of the normal welding state. However, weldments rarely achieve full reheat treatment performance.

4. Repair of welds and repair of weld defects

After a product has been welded, the welds with the following shape defects must be shaped:

(1) Large joints (that is, the stack height and width are very poor and unattractive);

(2) Tumors. Tumors are too much molten metal, mechanically stacked together, not fused with the parent metal, not part of the weld, must be shoveled;

(3) Welded joints at the arc of intermittent welding. The shaping tools generally use various shapes of the shovel sticks, so that the shape after repair is basically the same as that of the good welds, and the base material cannot be scratched or stabbed during the repair.

According to national standards, repairs must be made for weld defects that are not allowed.

The procedure for repairing is generally to first determine the scope of repair, and generally should extend 50 to 70 mm to both ends of the defect. If the root flaw detection result can be judged that the defect is close to the inner side or the outer side of the product, the side can be repaired first. If it cannot be judged which side it belongs to, it must be double-sidedly repaired. Generally, the outer side is repaired first, and the inner side is repaired first.

Before the repair, the defect must be excavated. If the air shovel is used, the height of the weld is flattened with a flat shovel, then the shovel is used to open the ditch. The depth of the ditch is to find the defect and remove the defect. Good metal. If the defect is large and the groove is too wide and too deep, it must be repaired first. After it is completely replenished, the groove is opened before the formal rework can be performed.

The repaired weld must be inspected and found to meet the standard requirements. It is best to return it once.