Performance analysis of magnesium alloy ordinary die-casting and vacuum die-casting parts based on F

Time：2023-10-24 21:17:52 / Popularity： / Source：

Die casting is the most commonly used forming process for magnesium alloys, accounting for approximately 90% of the total. During die-casting, magnesium alloy liquid fills mold very quickly, and its heat capacity is small. It is easy to form air entrainment during mold filling process, forming pores, also produces shrinkage and shrinkage cavities. Reducing pores, shrinkage porosity, shrinkage cavity defects in die castings and improving their density have always been focus of research. Vacuum die casting can reduce gas in mold cavity to a certain extent, reduce gas entrainment of casting, and improve its application range. Flow-3D software was used to simulate and analyze magnesium alloy radiator die-casting parts, compare defects and gas entrainment distribution positions of radiator vacuum die-casting parts and ordinary die-casting parts, conduct experimental verification to provide reference for production of magnesium alloy radiator die-casting parts. Simulate ordinary die-casting and vacuum die-casting of magnesium alloy radiators, compare defects and gas entrainment results of filling process, conduct product trial production. By analyzing microstructure and mechanical properties of ordinary die-casting and vacuum die-casting parts, it was found that vacuum die-casting can obtain magnesium alloy die-casting parts with complete mold filling and excellent appearance.

Graphical results

Radiator die-casting model and vacuum die-casting air extraction system are shown in Figure 1 (including gating system). Multi-cog type exhaust grooves are used to prevent metal liquid from blocking air extraction channel. Thermal physical properties parameters of AZ91D magnesium alloy used are shown in Table 1. Model was imported into simulation software and meshed, as shown in Figure 1b.

(a) Schematic diagram of die casting structure

(b) Mesh division of die casting parts

(c)Air extraction system
Figure 1 Structural diagram of AZ91D magnesium alloy die casting and cavity extraction system

Density/(g*cm-3)	Thermal conductivity/(Wm-1K-1)	Latent heat of fusion/(kJ*kg-1)	Specific heat capacity/(kJkg-1K-1)
1.702	84	341.6	1.42

Table 1 Thermophysical parameters of AZ91D alloy

Fast injection speed/(m*s-1)	Slow injection speed/(m*s-1)	Slow injection distance/mm	Injection specific pressure/MPa
4	0.2	120	84

Table 2 Process parameters of vacuum die casting AZ91D magnesium alloy

(a) t=0.0201s

(b) t=0.0339s

magnesium alloy radiator die-casting parts

(d)t=0.0509s
Figure 2 Filling process of ordinary die castings
Under process parameters in Table 2, surface defect simulation analysis was performed on ordinary die-casting parts and vacuum die-casting parts. Results are shown in Figure 3. It can be seen from simulation results that oxidized inclusions of ordinary die-casting parts are distributed in a wide range, mainly concentrated in the center and both sides of casting, and degree is higher than that of vacuum die-casting parts. Inclusion defects in vacuum die-casting parts are mainly concentrated in and near overflow groove. Overflow groove can be removed after forming. A small amount is distributed in the center of casting. Distribution range is small and degree of inclusion defects is low. Carry out gas field simulation analysis on ordinary die-casting parts and vacuum die-casting parts. Results are shown in Figure 4. It can be seen from simulation results that air entrainment area of ordinary die castings is mainly concentrated in the center of die casting, and there is also a small amount of air entrainment near runner. Amount of air entrainment is higher than that of vacuum die castings. Air entrainment area of vacuum die castings is mainly concentrated in overflow tank, with a small amount distributed in the central area of casting, and the overall air entrainment volume is small. It is found that structure of vacuum die casting is relatively dense.

(a) Ordinary die castings

(b) Vacuum die casting
Figure 3 Defect simulation results

(a) Ordinary die castings

(b) Vacuum die casting
Figure 4 Air entrainment simulation results
Under same process parameters, ordinary die-casting parts and vacuum die-casting parts were trial-produced respectively. Final die-casting parts are shown in Figure 5. It can be observed that appearance of ordinary die castings and vacuum die castings is relatively complete. However, since there is no vacuum in ordinary die-casting, die-casting parts inevitably have more air entrainment defects, which is particularly obvious after heat treatment. It can be seen from simulation results that defects and air entrainment of radiator die-casting are mainly concentrated in the center. Therefore, heat sinks at the same position of ordinary die-casting parts and vacuum die-casting parts were taken to prepare metallographic samples for comparative study. Macroscopic morphology of heat sink is shown in Figure 6.

Ordinary die castings

(b) Vacuum die casting
Figure 5 Macro photo of die casting

Figure 6 Heat sink

Figure 7 Microstructure of heat sink

Vacuum die casting		Ordinary die casting
σb/MPa	δ/%	σb/MPa	δ/%
227	5.4	199	3.8

Table 3 Comparison of mechanical properties between ordinary die castings and vacuum die castings

Analysis conclusion

(1) FLOW-3D software was used to perform filling simulation, defect field simulation and air entrainment simulation on ordinary die castings and vacuum die castings. It was found that oxidation inclusions and air entrainment of vacuum die castings were lower than those of ordinary die castings. Filling rules of AZ91D magnesium alloy radiator were obtained, as well as distribution of oxidation inclusions and gas entrainment defects.
(2) Through trial production, it is known that vacuum die-casting parts have a complete and good appearance and a dense structure. Tensile strength of vacuum die-casting parts is 14.1% higher than that of ordinary die-casting parts, and elongation rate is increased by 42.1%.

Gud Mould Industry Co., Ltd