Defects in alloy castings, etc., and defects are usually discovered after the parts are processed to meet the requirements. Therefore, it leads to the yield of magnesium alloy castings. Low-level questions:
(1) Coarse grain problem: The melting point of magnesium is low (651°C), but due to the fast heat conduction of the crystal, a relatively high-power heat source must be used, which makes the production of crystal alloy overheat and crystal grain.
(2) Oxidation and evaporation: The activity of glass is extremely high, and it is easily oxidized to form oxidized growth at high temperature. It has a high melting point (2500°C), high density (3.2g/cm3), and is easy to dye in the molten pool to form a solid state. Magnesium Alloy And, magnesium alloy case, also, also case. . . At high temperature, magnesium and magnesium are also easy to combine with air to form magnesium. The boiling point of magnesium and magnesium is not high (1100°C). At high temperature, calcium is easy to evaporate. Therefore, magnesium alloys need to be strictly protected when melting.
(3) Thermal stress: The thermal expansion coefficient of magnesium and its alloys is large, about 2 times that of steel and 1.2 times that of aluminum, so it is easy to cause large thermal stress, aggravate the generation of cracks and cause deformation of the workpiece.
(4) Cracks: Magnesium is easy to form low melting point eutectics with some alloying elements (such as Cu, Al, Ni, etc.), so the brittle temperature range is wide, and hot cracks are easy to form.
(5) Stomata: It is easy to produce hydrogen pores, and the solubility of hydrogen in magnesium decreases sharply with the decrease of temperature. When there are many sources of hydrogen, the tendency to appear pores is greater.
(6) Control of heat source: The heat source used must have sufficient energy rate, otherwise, when heating, the heat will be rapidly conducted to the substrate, ranging from too deep melting layer to melting of the entire substrate.
This makes the repair of magnesium alloys more difficult than ordinary materials.