Are you still worried about the defects of aluminum alloy quenching heat treatment?

In order to achieve the desired performance of the workpiece, aluminum alloy and other workpieces need to be quenched, tempered and other heat treatments. However, some common defects will inevitably occur during the heat treatment process. How will we solve these defects? Today, Zhengzhou Gou's will tell you about the experience gained from many years of working in the induction heating industry, hoping it will be helpful to you.

There are many kinds of defects caused by heat treatment of aluminum alloys, and the causes of defects are also various.

1. The manifestation of corrosion is mainly corrosion marks in the threads, fine grooves and small holes of the workpiece. The main reason is that all residual nitrate salts were not removed when the workpiece was cleaned after quenching. It should be carefully cleaned with hot water. However, when cleaning, you should pay attention to the pH of the cleaning water not being too high.

2. Bubbles mainly appear on quenched or annealed plates. The causes and methods are as follows:

(1) The lamination process of the aluminum cladding layer is improper, and there is a gap between the aluminum cladding layer and the basic material, with air or moisture remaining in between. When heated to high temperatures, the gas expands causing the aluminum cladding to bubble. The process should be standardized.

(2) There is lubricating oil, dirt and other dirt on the surface of the plate. Before heat treatment, the plate should be cleaned to keep the surface clean and free of dirt.

3. There are two main types of distortion, such as bending.

(1) After heat treatment, the shape and size of the workpiece change, such as warping and bending. The causes and solutions are:

1) Heating or cooling too fast can cause deformation of the workpiece due to thermal stress. Heating and cooling methods should be changed

2) Improper furnace loading, resulting in deformities during high temperature or quenching and cooling. Appropriate fixtures should be used and the method of launching the workpiece into the water should be correctly selected.

3) Straighten immediately after quenching

(2) Deformation of the workpiece after machining is mainly caused by the residual stress in the workpiece. After cutting, the stress is redistributed and deformed. Slow cooling media should be used to reduce residual stress or stress relief annealing should be used to prevent the occurrence of this defect.

4. Unsatisfactory mechanical properties

(1) The performance does not meet the indicators specified in the technical conditions,

1) There is a deviation in the chemical composition of the alloy. The heat treatment specifications should be adjusted according to the specific chemical composition of the workpiece material. The chemical composition of the next batch of castings should be adjusted.

2) Violation of heat treatment process regulations is usually due to the heating temperature not being high enough, the holding time not being long enough or the quenching transfer time being too long. Therefore, the holding time should be appropriately extended and the quenching transfer time should be reduced.

2. Low plasticity after annealing is mainly caused by low annealing temperature, insufficient holding time or too fast cooling rate after annealing to cause quenching. We should re-anneal.

5. Cracks: Visible cracks appear on the workpiece after heat treatment, usually at the corners, especially where the wall thickness is uneven. The main reasons are as follows:

(1) Complex shape, uneven wall thickness, and concentrated stress. The fillet radius should be increased, and reinforcing ribs can be added to the casting. Use asbestos to wrap parts that are too thin.

(2) The heating and cooling rates are too high. If excessive thermal stress causes cracking, it should be heated slowly and evenly, and a gentle cooling medium or isothermal quenching should be used.

(3) The casting already has microscopic or hidden cracks before quenching, which expand into visible cracks during the heat treatment process. The casting process should be improved to eliminate casting cracks.

6. Surface discoloration, mainly characterized by two defects:

(1) The gray-brown appearance of aluminum-magnesium alloys is mainly caused by high-temperature oxidation of aluminum-magnesium alloys with higher magnesium content. Defects can be controlled by heating by embedding alumina powder or graphite powder.

(2) The surface of aluminum alloy becomes gray after heat treatment.

1) The quenching liquid is too alkaline and the quenching liquid should be replaced.

2) Corrosive oil stains remain on the surface of the workpiece, leaving stains or traces of corrosion after evaporation.

3) There is too much water vapor in the air furnace, causing high-temperature oxidation. Bring as little moisture into the furnace as possible, and close the furnace door after the water vapor evaporates and escapes from the furnace.

7. Overheating

(1) Defect characteristics

1) When severe overburning occurs, the workpiece warps, and nodules and bubbles exist on the surface.

2) When LY12 alloy is slightly over-burned, the interface becomes coarse and hairy, and the strength and plasticity are increased. When it is severely over-burned, liquid spheres and over-burned triangles appear, and the strength and plasticity are reduced.

(2) Causes and elimination methods

1) There are too many impurities that form low-melting-point eutectics in cast aluminum alloys, and the charge should be strictly controlled. Due to the small amount of deformation and the concentration of eutectics in deformed alloys, the heating temperature should be lowered.

2) The temperature distribution in the furnace is uneven and the actual temperature exceeds the process specifications. The temperature distribution of the bath furnace or air furnace should be checked regularly

3) The heating rate of the casting alloy is too fast, and the unbalanced low melting point eutectic melts before it diffuses and disappears. It can be heated slowly with the furnace at a heating rate of 200-250℃/h, or it can be heated in sections.