In order to optimise the activation process, the effect of three activation processes on the direct electroless nickel-phosphorous plating on AZ91D was studied. The properties of the activation coating and Ni-P coating were characterised with electrochemical tests, SEM and EDX. The results showed that an optimum activation coating for nickel deposition was developed via twice activations of K 4 P 2 O 7 and NH 4 HF 2 respectively. The first activation in the K 4 P 2 O 7 solution could clean the surface and remove Mg 3 (PO 4 ) 2 dust produced by pickling. The coating with proper 1?12-1?49 F/O ratio (at-%) composed of MgF 2 and MgO or Mg(OH) 2 was produced via second activation in NH 4 HF 2 solution. Excess hydrogen produced by Mg with H þ in the plating bath could lead to high porosity and low adhesion of Ni-P coating. A compact Ni-P coating with better adhesion and corrosion resistance was explored in this research.

In this paper, research was conducted on a multivariate Bayesian variable sampling interval (VSI) control chart to address the problem of insufficient research in the area of Bayesian multivariate control charts with variable parameters. Bayesian multivariate control chart was constructed and control strategies on variable sampling interval and variable control limits were designed. Cost model was built and the corresponding parameters of cost and control chart were determined through researching in enterprise. Monte Carlo stochastic simulation was adopted to verify the economical and statistical advantages of Bayesian multivariate control chart. This study provides supports for in-depth study on Bayesian multivariate control chart with variable parameters.