Hot Compression Deformation Behavior Of Die-Cast AZ91D Magnesium Alloy

Publish Time: 04/02 2021 Author: Site Editor Visit: 11841

Due to its unique properties, the recognition of magnesium alloys in the industry continues to increase, and the scope of application is also expanding. At present, the main forming process of magnesium alloy is die-casting. In actual production, due to the needs of working conditions or process factors, it is often necessary to perform partial or overall plastic machining of magnesium alloy die castings. At the same time, the plastic machining of die castings can eliminate the shrinkage and porosity caused by the die casting process. , Improve the comprehensive mechanical properties of the material. However, magnesium alloys have poor plasticity and are difficult to perform plastic machining at room temperature; die-cast magnesium alloys are particularly difficult to perform plastic machining at room temperature due to the presence of a large number of near-network low-melting phases on the grain boundaries, and generally require thermoplastic machining. This limits the popularization and application of magnesium alloys to a certain extent.

In recent years, there have been many studies on the deformation behavior of magnesium alloys such as AZ31, AZ61, and AZ91 (non-die-cast state), but there are few reports on the deformation behavior of die-cast AZ91D magnesium alloy, especially the hot deformation behavior. In response to the above problems, this paper uses the Geeble-1500D thermal simulator to conduct a hot compression deformation experiment on the die-cast AZ91D magnesium alloy under the conditions of a strain rate of 0.01~10s -1 and a deformation temperature of 50~450℃ to study its Thermal compression deformation behavior; at the same time, the deformation microstructure was studied.

The main research work and results of the thesis are as follows:

Analyze and process the relevant data obtained from the hot compression experiment, and obtain the die-cast AZ91D magnesium alloy rheological curve; establish the high-temperature plastic deformation constitutive equation described by Zener-Hollomom parameters as έ=1.41×10 12 [sinh(0.014 σ)] 5.295 exp(-159449.509/RT), using hyperbolic sine function to determine the deformation activation energy of the material Q=159.45kJ·mol -1, compared with the gravity casting AZ91D magnesium alloy, its flow stress and deformation activation The lower energy may be caused by the obvious difference between the gravity casting state and the die casting state of the casting process.
According to the theory of dynamic material model and machining diagram, the power dissipation diagram, instability diagram and machining diagram of the die-cast AZ91D magnesium alloy were carried out using the experimental data of thermal compression and mathematical statistics software at strains of 0.3, 0.5 and 0.7. draw. Through the analysis of the power dissipation coefficient (η) and the instability coefficient (ξ(έ)) in the figure, it is determined that the deformation temperature is 260~350℃, the strain rate is 0.01~1s -1, which is the hot plastic machining of die-cast AZ91D magnesium alloy. The best machining area.
In the die-cast AZ91D magnesium alloy, there are more second phases distributed on the grain boundaries in a network. These second phases gradually dissolve in the matrix with the increase of the hot compression deformation temperature; the observation of the hot compression deformation structure of the die-cast AZ91D magnesium alloy shows that the deformation temperature, strain rate, and strain affect the hot compression deformation structure Significant; the structure difference in different areas of the same sample is more obvious, the deformation is larger in the center area near the sample, the streamlined band structure perpendicular to the compression direction produced by the structure is more obvious, and dynamic recrystallization occurs on the grain boundary. However, the amount of tissue deformation is small near the edge of the sample deformation, and the tissue grows simply.
Observation of the morphology of material die-casting defects in the process of hot compression deformation shows that hole-like defects are the main defects of die-cast magnesium alloys, and compression plastic deformation is an effective method to reduce the number of defects.

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