How to solve the brittleness of zinc alloy die castings?
Electrophoretic coating is an important process for displaying the gloss of Pearl Black profile. Firstly, the composition of bath solution should be stabilized, such as solid content, conductivity, molecular ratio of amine to acrylic acid, pH value, etc. At the same time, to ensure that the film thickness is appropriate, the orange peel thickness is too high, the orange peel thickness is low and glossy. Generally, it should be controlled at 7-9 microns. In addition, the voltage should not be too high, the pinhole vision of pure black surface paint film is easy to enlarge, so the voltage is lower than that of champagne and bronze, and should be controlled at 70-80V.
Surface treatment and composition:
Tool marks and wear marks on the surface of parts are the sources of stress concentration and crack growth. Therefore, after processing, it is necessary to strengthen the surface of the parts and grind them with fixtures to eliminate the hidden dangers on the surface of the parts. Some edges, sharp angles and holes of the workpiece are blunt and R-shaped. Generally speaking, the gray-white metamorphic hardening layer, brittle hardening layer and residual stress of 6-10 micron can be produced on the surface of electrical machining. The hardened layer should be removed by polishing and polishing the surface before use.
In the process of grinding and electrical processing, the workpiece will be magnetized to a certain extent, the magnetic force is very weak, and it is easy to absorb some small things. Therefore, before assembly, the workpiece should be demagnetized and the surface cleaned with ethyl acetate. In the assembly process, first refer to the assembly drawing, find out the parts, then list the equipment sequence between the parts, list the matters needing attention, and then assemble the die. Generally speaking, the guide sleeve of the guide pillar is installed first, then the die holder and the punching die are installed, and then the clearance of each part, especially the clearance between the punching die, is adjusted. After assembly, mould inspection should be carried out and general situation report should be prepared. For the problems found, we can adopt the method of reverse thinking, that is, from post-processing to forward processing, from finishing to rough processing, check one by one, until we find the crux of the problem and solve it.
There are many problems in the production process of zinc alloy die castings. One of the main problems is the lack of brittleness. The main manifestation is that the matrix metal grains are too large or too small, leading to easy fracture or fracture of castings. What happened? How can we solve this problem?
Firstly, the brittleness of zinc alloy die castings is mainly caused by impurities such as iron, tin, lead and zinc in zinc alloys used in production which are beyond the prescribed range, or by overheating or prolonged holding time of liquid alloys in production. E, which will lead to excessive coarsening of metal particles in the alloy matrix. On the contrary, supercooling of liquid alloy temperature will lead to too small grain size of casting metal.