What is the cause of black spots in aluminum die castings?

Aluminum die casting refers to casting aluminum or aluminum alloy heated to a liquid state into the cavity through sand mold or metal mold to obtain aluminum parts or aluminum alloy parts of various shapes and sizes. Let's talk about the polishing process of aluminum die castings and the causes and solutions of black spots on polishing

Aluminum die casting polishing process:

1. Mechanical polishing: refers to the use of physical methods, such as cutting, grinding, etc., to plastically deform the aluminum surface so that the convex parts of the surface fill the concave parts, thereby reducing and smoothing the aluminum surface roughness and improving the aluminum surface roughness. However, mechanical polishing leads to the destruction and deterioration of crystals on the metal surface, resulting in a plastically deformed layer, and the microstructure changes due to local heating.
2. Electrolytic polishing: Electrolytic polishing is to use a chemical reaction to immerse in the electrolytic cell with electrolytic polishing as the yang and insoluble metal as the yin. Through direct current, the anodic alumina dissolves, so that the alumina on the surface of the aluminum shell disappears from the aluminum shell and restores its luster.
3. Chemical polishing: Chemical polishing is chemical etching under special conditions. It is to control the selective dissolution of the aluminum surface, so that the microscopic raised parts on the aluminum surface are preferentially dissolved, so as to achieve the purpose of a smooth and bright surface.

Why are there black spots when aluminum die castings are polished?

• Oxidation: Aluminum has a high tendency to oxidize. When the aluminum surface is in contact with air, an oxide layer is easily formed. This oxide layer may not be easily removed during polishing, resulting in dark spots on the surface.
• Coating Residue: During the manufacture of aluminum die castings, coatings such as paint or coating protectants may be applied to protect the surface of the casting. These coatings may not be completely removed during polishing, leading to the formation of dark spots.
• Uneven material density: There may be uneven material density or inclusions in aluminum die castings. These inhomogeneities may manifest as dark spots or uneven surfaces during polishing.
• Rust or Contamination: If the aluminum die casting has rust or surface contamination, such as contact with other metals or exposure to chemicals, the polishing process may not be able to completely remove this rust or contamination, resulting in dark spots.
• Solutions to these problems may include using proper polishing processes and materials, removing coating residues, employing better material and manufacturing process controls, and ensuring surface quality and clarity during casting fabrication.

How to solve the problem of black spots when aluminum die castings are polished?

Solving the problem of black spots when polishing aluminum die castings may require comprehensive consideration of multiple factors, and appropriate adjustments and experiments. The final solution should be tailored to the specific situation, evaluated, and optimized according to the actual situation.

• Surface Preparation: Proper surface preparation is key before proceeding to polish. Ensure that the surface of the aluminum die casting is clean and remove any oxide layer, coating residue, contaminants, etc. Surface irregularities can be removed by cleaning with suitable detergents or solvents, or by mechanical methods such as grinding.
• Polishing process selection: It is very important to choose the appropriate polishing process and tools. Polishing is done using suitable abrasives and polishing materials, as well as proper speed, pressure, and lubricants. Depending on the specific situation, different polishing methods can be tried, such as manual polishing, mechanical polishing, or chemical polishing, to find the most suitable method.
• Control polishing time and temperature: Excessive polishing time or high polishing temperature may cause overheating and oxidation of the aluminum surface, resulting in dark spots. Control polishing time and temperature to ensure proper polishing conditions.
• Improving Materials and Manufacturing Processes: If black speck is a frequent occurrence, improved material selection and manufacturing processes may need to be considered. Choose a purer aluminum material to reduce inclusions and unevenness. At the same time, casting and machining processes are optimized to reduce surface defects and contamination.

Material requirements for aluminum alloy die castings

1. Good adsorption;
2. Good performance;
3. The hardness also needs to be high;
4. Good toughness;

Storage conditions of aluminum alloy die castings

1. The storage place should be dry and ventilated;
2. Avoid exposure to chemical elements;
3. Avoid direct sunlight;
4. The storage position can avoid damage to zinc alloy die castings.