Preparation Of Cu-Si Composite Powders By Electroless Plating Method

The object of this experiment is to obtain Cu-Si composite materials with better performance by the way of preparing Cu-Si composite powder. During the period of the preparation of the metal-matrix composite, composite powder could enhance the degree of uniform mixing of the matrix and the reinforced phase, decrease the interface residual stress and improve the heterogeneous combination status.To prepare Cu–Si composite powder which is coated uniformly and has good performance, the preliminary process of preparation of Cu–Si composite powder by electroless plating method was firstly investigated. The experiments suggest that: when only the copper salt (CuSO4·5H2O), reducing agent (HCHO), complexing agent (EDTA·2Na and Na2C4H4O6) in bath and silicon powder are not coarsened, the Cu–Si composite powder is prepared successfully; when the concentrations of CuSO4·5H2O, HCHO and complexing agent are changed in multiples of the same, the Cu–Si composite powder with different contents of Cu could be prepared; when silicon powder is coarsened and HCHO is added by dropping, the Cu–Si composite powder is better.And then, the process of preparation of Cu–Si composite powder by electroless plating method was studied by orthogonal design theory. The optimal conditions of the electroless copper plating process are obtained as follows: HCHO/Cu of 6, complexing agent /Cu of 2, EDTA·2Na/ complexing agent of 2/5, pH value of 12 and temperature of 60℃. In other words, when the concentration of Cu2+ is 0.05mol/L, the optimal conditions of the electroless copper plating process are as follows: CuSO4·5H2O of 30g/L, HCHO of 72.0ml/L, EDTA·2Na of 35.735g/L, Na2C4H4O6 of 40.640g/L, pH value of 12~12.5 and temperature of 60℃.In this experiment, a number of deposition parameters such as the pH value, the temperature and the concentration of the bath were studied. The results are as follows: (1) High pH is beneficial to the proceeding of the reaction of electroless plating and the shortening of the reaction time, but adverse to uniform coating; low pH is helpful to the improving of the quality of the coating, but too low pH prolongs the reaction time. (2) The reaction time shortens sharply by increasing the concentration of HCHO, but when exceeding certain concentration, the reaction time isn't sensitive to the change of concentration ; and the concentration of HCHO is a necessary condition for good coating. (3) Increasing the temperature helps to enhance the reaction rate and shorten the reaction time; but when the temperature is excessively high, the bath stability decreases and there are some pure coppers in the composite powder. (4) The Cu-Si composite powder, which is coated well and uniformly, can be prepared in the short time, when the conditions of the electroless copper plating process are CuSO4·5H2O of 30g/L, EDTA·2Na of 35.735g/L, Na2C4H4O6 of 40.640g/L, HCHO of 60-72ml/L, temperature of 60℃, pH of 12-12.5, the bath load of 1.5g/100ml.The cross section of the Cu-Si composite powder was investigated. The results are as follows: the prepared powder is Cu-Si composite powder with 5.5μm thick coating. Si powder and copper layer combined closely as a result of a Cu-Si coexisting layer with 4μm thickness, which is beneficial to the performance of Cu-Si composite materials.