Development Of Continuous Solderable Electroplating Process On Aluminum Strip And Research On Key Technologies

In this dissertation, the research was conducted on continuous solderable electroplating on aluminum and aluminum alloy strip. The productive process was tracked closely and the matters emerged during the process was settled off through combined experiments in the workshop and laboratory carried by our group as well as the staff on spot. The solderable aluminum products that possessed high and reliable performance were finally acquired.In order to solve the problem that the bad adhesive force of nickel-plate in the top part of the aluminum strip appeared in nickel plating process, addition of Glycerin in zincate solution was first reported in consideration of its moisturizing function to improve the adhesive force of upper electroplating nickel layer. Method of observing liquid mark on pH test paper, time-potential curve measurement and thermal shock followed by cross cut test were utilized to study the retained liquid film distribution, the potential development of zincate film and adhesive force of electroplating nickel coat on aluminum substrate respectively after one time zincate immersion with different concentration of Glycerin in zincate solution. It indicated that the retained liquid film became well-distributed when20g/L Glycerin was added and oxidation of the upper zincate layer caused by liquid film drying was conquered to guarantee the well-adhesion of successive electroplating coating.A cyanide-free zincated solution with four kinds of alloy compositions was developed to eliminate dark spots on nickel coat. The USB electronic microscope was utilized to observe the surface of aluminum alloy sample after zincation dispose. Comparing with commercially available zincate solution, the solution mentioned above could achieve a compact and well-proportioned zincation layer with fine grains. Consequently, the surface defects of dark spots and stripes caused by zinc ions impurities in the plating bath which could be dated from chemical dissolution of bulky zinc grains in acid solution.The treatment process was simplified during the period of production practice. The optimized time-saving, labor-saving and cost-saving process was alkaline degreasing, acid etching, one step zincation and nickel electroplating, and nickel coating aluminum strip that possessed solderability was acquired.OCA video contact angle measuring apparatus and optical microscope with high times was used to observe and measure the wetting angles of SAC soldering flux on nickel coating. Both the two measurement results of the two methods were around11°. This can satisfy the well weldability standard "θ≤30°" mentioned in solderability classification standard. The joint shear strength of soldering aluminum strip was measured by universal testing machine and the morphology of weld interface between aluminum strip was observed by SEM. It indicated that the fine solder ability of nickel coated aluminum strip was up to the grade of requirement of radiators absolutely.Aiming at lowering the cost and reducing the pollution in solderable electroplating process of aluminum substrate, the technology of iron plating in ferrous sulphamate bath system as nickel substitute after zincation process was achieved in this paper. The iron electroplating coating was regard as a interlayer which was going to covered by solderable coats such as tin or copper coat in the subsequent processes. Technical conditions such as bath pH, operating temperature and bath compositions were optimized through Hull cell test. The adhesion, corrosion behavior and solderability of the corresponding coatings acquired in the optimum conditions were characterized respectively. It indicated that sulphamate iron plating technology could achieve well coating adhesion and solder wetting ability of tin-plating layer though the anti-corrosion behavior is not so well.