In order to explore an effective way to shorten treatment time and enhance the quality of treatment coating, AC micro-arc oxidation was conducted to treat the surface of AZ31 B deformation magnesium alloy in KF+KOH treatment solution. The infl uences of micro-arc oxidation parameters such as concentration of KF, concentration of KOH, output voltage of booster, temperature of treatment solution, and treatment time on treatment coating thickness were raveled out under different conditions. The structure and composition of treatment coating were determined, the growth mechanism of treatment coating was discussed, and the quick surface treatment technology for compact treatment coating with maximum thickness was developed. The experimental results show that: A maximum 33 μm-thick compact treatment coating, consisting of MgF2 and MgO mainly, can be formed on AZ31 B in 112 s under the conditions of 1 132 g/L KF, 382 g/L KOH, 66 V for output voltage of booster and 34 ℃ of treatment solution which were optimized by a genetic algorithm from the model established by artifi cial neural networks. There are no "crater-shaped" pores in this treatment coating as the heat shock resulting from the smooth variation of AC sinusoidal voltage is far smaller than that of the rigidly varied DC or pulse current. The treatment time is only one sixth of that adopted in the other surface treatment technology at best, principally for the reason that the coating can always grow irrespective of the electric potential of AZ31 B. This investigation lays a fi rm foundation for the extensive application of magnesium alloy.
A straight-blade mechanical stirrer was designed to stir A356-3.5vol%SiC p liquid in a cylindrical crucible with the capability of systematically investigating the influence of rotating speed of stirrer on the distribution of SiC particles in A356 liquid.The experimental results show that the vertical distribution of SiC particles in A356 liquid can be uniform when the rotating speed of stirrer is 200 rpm,but the radial distribution of SiC particles in A356 liquid is always nonhomogeneous regardless of the rotating speed of stirrer.The radial centrifugalization ratio of SiC particles in A356 liquid between the center and the periphery of crucible increases with the rotating speed of stirrer.The results were explained in the light of SiC particles motion subject to a combination of stirring and centrifugal effect.
The tilt-blade mechanical stirring of A356-2.5vol.%SiCp liquid was conducted in a cylindrical crucible to solve the problem of nonhomogeneous radial distribution of SiC particles in conventional straight-blade mechanical stirring. The radial distribution of SiC particles in A356 liquid was studied under the conditions of 25° for horizontal tilt angle α of the blade, 200 r/min for rotating speed of stirrer and 10 mm/s for speed of moving up and down of stirrer. The results show that there exists a nonlinear relationship between circumferential tilt angle β of the blade and radial relative deviation d of SiCp content in A356 liquid. When β is smaller than 26°, the d of SiCp content in A356 liquid between the center and the periphery of crucible decreases with increasing β. Conversely, when β is bigger than 26 , d increases with increasing β. Only when β is about 26°, d can be equal to nought i.e. uniform radial distribution of SiC particles can be realized. It can be seen that the nonhomogeneous radial distribution of SiC particles in conventional straight-blade mechanical stirring can be eliminated in this tilt-blade mechanical stirring of A356-SiCp liquid.
Yunhui DUPeng ZHANGYujie WANGJun ZHANGShasha YAOChengyu LI
The mechanical stirring of A356-2.5 vol.% SiC p liquid was conducted in a cylindrical crucible by a straightblade stirrer.The radial distribution of SiC particles in A356 liquid was studied under the conditions of 25 deg.for gradient angle α of blade and 10 mm/s for speed of moving up and down of stirrer.The results show that there exists a nonlinear relationship between rotating speed of stirrer and radial relative deviation of SiC p content in A356 liquid between the center and the periphery of crucible.The greater the rotating speed of stirrer is,the bigger the radial relative deviation of SiC p content in A356 liquid becomes and the more nonhomogeneous the radial distribution of SiC particles in A356 liquid turns.In addition,when the rotating speed of stirrer is about 200 r/min,the vertical distribution of SiC particles in A356 liquid is relative uniform.It can be seen that the nonhomogeneous distribution of SiC particles in A356 liquid results from the nonhomogeneous radial distribution of SiC particles in A356 liquid in straight-blade mechanical stirring ultimately.
