The purpose of this study was to improve tensile properties by grain refinement technique for injection molding of magnesium alloy by using solid carbon materials. A solid carbon material of Carbon Black was attached to surface of AZ91D alloy chips by using ball-milling. AZ91D alloy chips and Carbon Black were mixed while heating and stirring in the cylinder of magnesium injection molding machine, then molten metal was injection molded to 2.5 mm thick flat plate. The mechanical characteristics of molded products were evaluated uniaxial tensile load. The tensile test result showed that the 0.2% of proof stress, tensile strength and fracture strain were improved by Carbon Black addition. Microstructure observation revealed that the grain size of molded products were progressively finer when Carbon Black addition was increased. These results suggested that the addition of appropriate amount of Carbon Black is effective to improve the tensile properties of AZ91D alloy.

The influence of molding conditions on the strength of the magnesium alloy products formed using an injection molding method was examined. Test pieces were cut from a plain plate made of AZ91D, which was molded in a metal die using a Thixomolding machine. The test piece, whose thickness was 2.5 mm, was examined. The barrel temperature was varied from 873 to 903 K, and the gate velocity was varied to the extent possible, between 11.4 and 28.7 m/s. The mold temperature ranged from 423 to 483 K. The test pieces performance was determined using a tensile test. The main results obtained are as follows. The calculated average roughness decreased when the gate velocity increased. The tensile strength improved because the chill rate increased when the temperature of the mold decreased. The 0.2% proof strength was not influenced by the shooting conditions in this study. The tensile strength and the elongation to fracture depended strongly on the gate velocity.

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