Several common methods of electroplating of die casting aluminum alloy die castings
2021-08-23
The electroplating pretreatment of die-casting aluminum/aluminum alloy die-casting includes four important processes: degreasing, acid etching, chemical plating or displacement plating, and pre-plating. The key is electroless plating or displacement plating. Therefore, the experiments that are often done will be concentrated on this process. Of course, different aluminum materials and different processing methods have different requirements for pre-processing. For example, the pre-processing of die-cast aluminum parts and rolled aluminum parts are very different, and even if it is the same processing method, different aluminum materials have different requirements. For example, the copper content of aluminum directly affects the bonding force of its coating. The experiment of the pre-treatment plan for the electroplating of die-cast aluminum parts is also a systematic comparison experiment. It is necessary to process the samples with different selected pre-treatment processes, and then perform the same electroplating process, and then test the bonding force. The key to this kind of comparison experiment is to ensure that, except for different process points, other processes are under the same conditions, otherwise there will be no comparability and no comments can be made.
Four common methods for electroplating of die-cast aluminum parts:
Aluminum phosphating
After selecting methods such as SEM, XRD, potential-time curve, film weight change, etc., the effects of accelerators, fluorides, Mn2+, Ni2+, Zn2+, PO4; and Fe2+ on the phosphating process of aluminum have been specifically studied. The study showed that: Guanidine nitrate has the characteristics of good water solubility, low dosage, and rapid film formation. It is a useful accelerator for aluminum phosphating: fluoride can promote film formation, increase film weight, and refine grain; Mn2+, Ni2+ can be significant By refining the crystal grains, the phosphating film can be made uniform and dense, and the appearance of the phosphating film can be improved; when the Zn2+ concentration is low, the film cannot be formed or the film formation is poor. As the Zn2+ concentration increases, the O4 content of the film will increase the weight of the phosphating film. The impact is greater, increasing the content of PO4. The weight of the phosphating film increases.
Alkaline electrolytic polishing process of aluminum
The alkaline polishing solution system was studied, and the effects of corrosion inhibitors, viscosity agents, etc. on the polishing effect were compared. An alkaline solution system with a good polishing effect on zinc-aluminum die castings was successfully obtained, and for the first time, it was obtained that the operating temperature can be lowered. , Prolong the service life of the solution, and at the same time can improve the polishing effect. The results of the experiment indicate that adding appropriate additives to the NaOH solution can produce a good polishing effect. Exploratory experiments also found that after DC constant voltage electrolytic polishing with glucose NaOH solution under certain conditions, the reflectivity of the aluminum surface can reach 90%, but due to the unstable factors in the experiment, further research is needed. The feasibility of using the DC pulse electrolytic polishing method to polish aluminum under alkaline conditions was explored. The results indicate that the pulse electrolytic polishing method can achieve the leveling effect of DC constant voltage electrolytic polishing, but its leveling speed is slow.
Aluminum and aluminum alloy environmentally friendly chemical polishing
Determined to develop a new environmentally friendly chemical polishing technology with phosphoric acid-sulfuric acid as the base fluid, which must achieve zero emission of NOx and overcome the quality shortcomings of similar technologies in the past. The key to the new skill is to add some special compounds to the base fluid to replace nitric acid. For this reason, the primary need is to analyze the three-acid chemical polishing process of aluminum, especially the key points to study the role of nitric acid. The primary role of nitric acid in aluminum chemical polishing is to suppress pitting corrosion and improve polishing brightness. Combined with the chemical polishing experiment in simple phosphoric acid-sulphuric acid, it is thought that the special substances added to phosphoric acid-sulphuric acid should be able to suppress pitting corrosion and slow down the overall corrosion. At the same time, it is necessary to have a better leveling, smoothing and brightening effect.
Electrochemical surface strengthening treatment of aluminum and its alloys
Four common methods for electroplating of die-cast aluminum parts:
Aluminum phosphating
After selecting methods such as SEM, XRD, potential-time curve, film weight change, etc., the effects of accelerators, fluorides, Mn2+, Ni2+, Zn2+, PO4; and Fe2+ on the phosphating process of aluminum have been specifically studied. The study showed that: Guanidine nitrate has the characteristics of good water solubility, low dosage, and rapid film formation. It is a useful accelerator for aluminum phosphating: fluoride can promote film formation, increase film weight, and refine grain; Mn2+, Ni2+ can be significant By refining the crystal grains, the phosphating film can be made uniform and dense, and the appearance of the phosphating film can be improved; when the Zn2+ concentration is low, the film cannot be formed or the film formation is poor. As the Zn2+ concentration increases, the O4 content of the film will increase the weight of the phosphating film. The impact is greater, increasing the content of PO4. The weight of the phosphating film increases.
Alkaline electrolytic polishing process of aluminum
The alkaline polishing solution system was studied, and the effects of corrosion inhibitors, viscosity agents, etc. on the polishing effect were compared. An alkaline solution system with a good polishing effect on zinc-aluminum die castings was successfully obtained, and for the first time, it was obtained that the operating temperature can be lowered. , Prolong the service life of the solution, and at the same time can improve the polishing effect. The results of the experiment indicate that adding appropriate additives to the NaOH solution can produce a good polishing effect. Exploratory experiments also found that after DC constant voltage electrolytic polishing with glucose NaOH solution under certain conditions, the reflectivity of the aluminum surface can reach 90%, but due to the unstable factors in the experiment, further research is needed. The feasibility of using the DC pulse electrolytic polishing method to polish aluminum under alkaline conditions was explored. The results indicate that the pulse electrolytic polishing method can achieve the leveling effect of DC constant voltage electrolytic polishing, but its leveling speed is slow.
Aluminum and aluminum alloy environmentally friendly chemical polishing
Determined to develop a new environmentally friendly chemical polishing technology with phosphoric acid-sulfuric acid as the base fluid, which must achieve zero emission of NOx and overcome the quality shortcomings of similar technologies in the past. The key to the new skill is to add some special compounds to the base fluid to replace nitric acid. For this reason, the primary need is to analyze the three-acid chemical polishing process of aluminum, especially the key points to study the role of nitric acid. The primary role of nitric acid in aluminum chemical polishing is to suppress pitting corrosion and improve polishing brightness. Combined with the chemical polishing experiment in simple phosphoric acid-sulphuric acid, it is thought that the special substances added to phosphoric acid-sulphuric acid should be able to suppress pitting corrosion and slow down the overall corrosion. At the same time, it is necessary to have a better leveling, smoothing and brightening effect.
Electrochemical surface strengthening treatment of aluminum and its alloys
The process, function, description, composition and structure of the anodic oxidation and accumulation of aluminum and its alloys in a neutral system to form a ceramic-like amorphous composite conversion coating have begun to explore the film formation process and mechanism of the coating. The results of the process study indicate that in the Na_2WO_4 neutral mixing system, the concentration of the film-forming accelerator is controlled to be 2.5—3.0g/l, the concentration of the complexing film agent is 1.5—3.0g/l, and the concentration of Na_2WO_4 is 0.5—0.8 g/l, peak current density is 6——12A/dm——2, weak mixing, can obtain a complete, uniform, and good-gloss gray series inorganic non-metallic film. The thickness of the film is 5-10μm, the microhardness is 300-540HV, and the corrosion resistance is excellent. The neutral system has good adaptability to aluminum alloys, and can form a good film on various series of aluminum alloys such as rust-proof aluminum and forged aluminum.
