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Magnesium alloy castings often exist air holes, inclusions and other defects, and these defects are usually machined to the required size of the required to be found, so lead to low yield of magnesium alloy castings. In the process of repairing the defect of magnesium alloy, the following problems are faced:

(1) coarse grain problem: the melting point of magnesium is low (651 degrees C), but because of the fast heat conduction, it is necessary to use a high power heat source, which makes it easy to overheat and grain growth.

(2) oxidation and evaporation: the activity of magnesium is very high, it is easy to be oxidized at high temperature to form Magnesium Oxide, its high melting point (2500 degrees C), high density (3.2g/cm3), in the molten pool is easy to form a small sheet of solid slag. Moreover, the magnesium alloy in the absence of oxygen isolation, but also easy to burn. Nitrogen combine to form magnesium at high temperature magnesium also easily and in the air, so that the bad performance of the melting zone after cooling. The boiling point of magnesium is not high (1100 degrees Celsius), high temperature, magnesium is easy to evaporate. So magnesium alloys need to be strictly protected when melting.

(3) thermal stress: magnesium and its alloy thermal expansion coefficient is larger, about 2 times of steel, 1.2 times of aluminum, so easy to cause a large thermal stress, and increase the production of cracks and causing deformation of the workpiece.

(4) crack: magnesium is easy to form low melting eutectic with some alloying elements (such as Cu, Al, Ni, etc.), so the brittleness temperature range is wide, and it is easy to form thermal crack.

(5) porosity: easy to produce hydrogen porosity, the hydrogen solubility in magnesium decreased with the temperature, and when the source of hydrogen is more, the tendency of porosity is bigger.

(6) the heat source control: the heat source must have enough energy, otherwise in the heating, the heat will quickly transfer to the substrate, ranging from melting is too deep, while the substrate melting.

This makes it more difficult to repair the magnesium alloy than the ordinary materials.