What surface treatment is required for aluminum alloy die casting?

1. Aluminum phosphating

The effects of accelerant, fluoride, Mn2+, Ni2+, Zn2+, PO4 and Fe2+on the phosphating process of aluminum were studied in detail by means of SEM, XRD, potential time curve and film weight change.

The results show that guanidine nitrate has the characteristics of good water solubility, low dosage and fast film formation. It is an effective accelerator for aluminum phosphating. Fluoride can promote film formation, increase film weight and refine grains; Mn2+and Ni2+can obviously refine the grains, make the phosphating film uniform and compact, and improve the appearance of the phosphating film; When the concentration of Zn2+is low, the film cannot be formed or the film is poor. With the increase of the concentration of Zn2+, the film weight increases; The content of PO4 has a great influence on the weight of phosphating film and increases PO4. The content increases the weight of phosphating film.

2. Alkaline electrolytic polishing of aluminum

The alkaline polishing solution system was studied, and the effects of corrosion inhibitor and viscosity agent on the polishing effect were compared. The alkaline solution system with good polishing effect was successfully obtained, and the additives that can reduce the operating temperature, prolong the service life of the solution and improve the polishing effect were obtained. The experimental results show that adding proper additives in NaOH solution can produce good polishing effect.

The exploratory experiment also found that the reflectivity of aluminum surface could reach 90% after DC constant voltage electropolishing with NaOH solution of glucose under certain conditions. However, due to the unstable factors in the experiment, further research is needed.

The feasibility of using DC pulse electropolishing method to polish aluminum under alkaline conditions is explored. The results show that the pulse electropolishing method can achieve the leveling effect of DC constant voltage electropolishing, but the leveling speed is slow.

3. Environmentally friendly chemical polishing of aluminum and aluminum alloys

It is determined to develop a new environment-friendly chemical polishing technology with phosphoric acid monosulfuric acid as the base liquid. This technology should achieve zero emission of NOx and overcome the quality defects of previous similar technologies. The key of the new technology is to add some compounds with special effects to the base solution to replace nitric acid.

Therefore, it is necessary to analyze the process of aluminum tri acid chemical polishing, especially the role of nitric acid. The main role of nitric acid in aluminum chemical polishing is to inhibit spot corrosion and improve polishing brightness.

Combined with the chemical polishing test in simple phosphoric acid monosulfuric acid, it is considered that the special substances added in phosphoric acid monosulfuric acid should be able to inhibit spot corrosion, slow down overall corrosion, and must have good leveling and brightening effects

4. Electrochemical surface strengthening of aluminum and its alloys

The process, properties, morphology, composition and structure of ceramic like amorphous composite conversion film formed by anodic oxidation deposition of aluminum and its alloys in neutral system are discussed.

The results of the process study show that_ 2WO_ 4. In the neutral mixed system, the concentration of film forming accelerator is controlled to be 2.5 ～ 3.0g/l, the concentration of complex film forming agent is 1.5 ～ 3.0g/l_ 2WO_ 4. The concentration is 0.5 ～ 0.8g/l, the peak current density is 6 ～ 12A/dm~2, and weak stirring can obtain a complete and uniform gray series inorganic non-metallic film with good luster.

The film thickness is 5-10 μ m. The micro hardness is 300 ～ 540HV, and the corrosion resistance is excellent. The neutral system has good adaptability to Dalian aluminum alloy die-casting. The film can be formed on various series of aluminum alloys such as rust proof aluminum and forged aluminum.