Microstructure And Properties Of Rapidly Solidified Magnesium Alloy

In order to obtain the high property rapidly solidified magnesium alloys with simple technique, the influence of solidified velocity on the microstructures and properties of rapidly solidified AZ91 magnesium alloys and the relation between microstructures and mechanical properties of rapidly solidified AZ91 magnesium alloys were investigated in this paper. The rapidly solidified AZ91 magnesium alloys were made in vacuum quenching furnace. First the common as-cast AZ91 magnesium alloys were remelted. Then the melt alloys were respectively cooled in water, saturated brine, dry ice and liquid nitrogen. And the rapidly solidified AZ91 magnesium alloys bars under different cooling rates were gotten. The microstructures, phase compositions, phase components and compression properties of rapidly solidified AZ91 magnesium alloys bars and common as-cast AZ91 magnesium alloys under room temperature were studied with optical microscope, X-ray diffraction analysis, energy spectrum analysis and electron omnipotence testing machine. Artificial aging heat treatment was used in rapidly solidified AZ91 magnesium alloys cooled with liquid nitrogen owing to its the most solid solubility and microstructure and strength properties testing were researched.The results showed that the solid solubility phase increased with the increasing cooling rate, and the fraction of Mg₁₇Al₁₂ decreased. The single phase of the solid solubility can be obtained under the cooling condition of liquid nitrogen. To rapidly solidified AZ91 magnesium alloys, the element Zn distributes in the second phase only, to as-cast AZ91 magnesium alloys, the element Zn distributes in both the second phase and the matrix. The compression strength of rapidly solidified AZ91 magnesium alloys decreased with the increasing cooling rate, but still higher than those of cast conditions. After artificial aging heat treatment, compression strength of the rapidly solidified AZ91 magnesium alloy cooled with liquid nitrogen was obviously improved, due to the precipitation of the second phase. Compression rupture strength of the rapidly solidified AZ91 magnesium alloys cooled with liquid nitrogen is 253.5MPa, while the compression rupture strength of AZ91 magnesium alloys cooled with liquid nitrogen after artificial aging heat treatment increased to 335.3MPa. Compression yield strength of themincreased from 138.1MPa to 225.91MPa. The aging treatment process of the rapidly solidified AZ91magnesium alloys cooled with liquid nitrogen is 168°C/14h. The elevation of compression strength of rapidly solidified AZ91 magnesium alloys were affected by both the second phase strengthening and solid solution strengthening. But the second phase strengthening take the main part in the elevation of compression strength.