4 influence the quality of coating frictional reducing bearing the factors
4.1 lead tin copper two-metals friction ternary alloy plating solution of the literature of formulation and process parameters
Reference [3 ~ 10, 20, from 23 to 24] published in lead tin copper ternary alloy plating on the composition of the content and the process parameters summarized as follows:
Pb2 + (in Pb (BF4) 2 form to join) : 80 ~ 333 g/ι;
Sn2 + (Sn (BF4) 2 form to join) : 5 ~ 33.3 g/ι;
Cu2 + (to Cu (BF4) 2 form to join) : 2 ~ 11 g/ι;
HBF4 (free) : 40 ~ 300 g/ι;
H3BO3 (free) : 15 ~ 40 g/ι;
Stabilizer: 2 ~ 12 g/ι;
Additives: 0.1 ~ 5 g/ι;
Cathodic current density (DK) : 1 ~ 8 A/dm2;
Temperature (T) : 15 ~ 30 ℃;
Time (t) : 15 to 35 min;
The plating thickness (δ) : 15 to 30 μ m;
The anode composed: PbSn8 to 11.
4.2 influence the quality of coating related factors reducing friction
From the above formula can see, whether component content or process parameters, its range are too broad; To adapt to the production requirements, it is necessary to further optimization, the optimization in test before plating quality frictional reducing influence of relevant factors make the necessary analysis to determine the orthogonal experiment in each factor levels of the feasible region.
2 the Lord salt ion of concentration
The bath salt ion for Pb2 Lord +, and Sn2 +, Cu2 +. One of the Sn2 Cu2 + +, and the content of the alloy coatings according to the weight of Sn, Cu percentage content for the corresponding adjustment, can satisfy user coating constituents content requirements. So the Lord salt ion is concerned, is the only solution Pb2 + content on the influence on the quality of coating is discussed.
The solution Pb2 + for alloy cladding provides the main components, reports in the literature of the scope for 80 ~ 333 in g/ι. If the high concentration, they will be allowed to use higher cathodic current density, sedimentary speed; But scattered capacity reduction, out of the loss is bigger. If the concentration is low, the scattered ability is good, but deposition at a slower speed. If too low in the bath is strong bad polarization is too big, the current rise not to go up, there is air stripe coating defects and LengZhui form of microscopic analysis of metallographic structure, intuitive shows in coating of rough. If the content is high on the solution to bring out loss increases, increase the cost; On the other hand in air temperature is lower vulnerable to boric acid (H3BO3) and additives separation phenomenon, causing the coating of rough. Suitable content is to process the cap on the provisions DK, coating and crystallization meticulous; In the temperature drop to 15 ℃ below, the plating boric acid and additives should be no separation phenomenon.
Out free fluorine boric acid (HBF4) of concentration
Its main function is to make the anode normal dissolve; Prevent bivalent tin (Sn2 +) oxidation and inhibit major ions (Pb2 +, Sn2 +, Cu2 +) hydrolysis, improve the stability of the solution; Improve the sex and the scattered ability; Refining the crystal.
Reports in the literature of the range of content 40-300 g/ι.
When the content of free fluorine boric acid too low, well it out of the hydrogen ions (H +) low concentration, the plating may occur as follows hydrolysis reaction;
Pb2 + + 2 H2O < = = > Pb (OH) 2 + 2 H + press
Sn2 + + 2 H2O < = = > Sn (OH) 2 + 2 H + press
Cu2 + + 2 H2O < = = > Cu (OH) 2 + 2 H + press.
They generate hydrogen chloride precipitation and suspended in the plating. Electroplating, they adhesion on the surface of the matrix or inclusion in the coating, making the coating and the magnesium substrate bond between the decline, and coating sent fragile, rough, the tabby, thus the wear resistance of the coating and anti-fatigue strength performance obviously decreased.
When the free fluorine boric acid bath content is high, with a high in current density place, namely suitable place or inspecting the cutting edge, end, etc have hydrogen exhalation. The result is in bearings coated top produce airflow stripe and pinhole defect. At the same time, because the edge effect and so that the high point discharge current density in sedimentary too fast, the bath salt ions added to the Lord, the surface spread or nucleation control into a liquid mass transfer control, strong bad polarization that bush increased internal surface (cathode) occurred the following electrochemical side effects:
2 H + + 2 e < = = > H2 ↑
From the above reactions can see, when hydrogen ions (H +) concentration (namely the corresponding free fluorine boric acid concentration) increase as, balance to the right move, promote the formation of hydrogen (H2). The results of the formation of hydrogen will not only make coating appear airflow stripe and pinhole defect, etc, but also because of the ChuShengTai hydrogen (H-that the hydrogen radical) coating to metal hydride and internal penetration form produced distortions and thread lattice dislocation phenomenon. If by scanning electron microscope (SEM) watch this coating sections of microstructure, can be found in the crystal structure of the big LengZhui [7], intuitively coating is rough. On the other hand, the formation of metal hydride is not stable material, the baking heat when inspection and release the decomposition hydrogen (H2) and so make coating happen blister phenomenon.




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