| dc.description.abstract | This study investigates low-pressure casting experiments of A356 (Al-Si-Mg) aluminum alloy castings with varying thicknesses. The objective is to explore the flow filling and oxide film formation conditions and mechanisms in practical casting applications. By adjusting casting parameters such as low-pressure casting pressure, pressurization time, and mold preheating temperature, the study examines the issues of filling flow fronts. The findings are validated and analyzed using MAGMA 5.5 simulation software.
The experiments reveal that thicker castings exhibit better mechanical properties due to adequate holding pressure and complete filling, which provide sufficient dendritic arm spacing compensation. In contrast, 2.8 mm thick plates experience unstable flow at the tail end of the aluminum melt due to excessive pressure during mold filling, causing wave entrainment and air entrapment. This results in air and oxide film accumulation in the midsection of the test specimen, leading to poorer mechanical properties. Key findings are summarized as follows:
For 2.8 mm thick aluminum alloy plates in low-pressure casting, the proportion of wave entrainment and splashing is higher on the left side than on the right. Air entrapment forms at the mold entrance and propagates through the entire specimen, reducing mechanical properties on the left side compared to the right.
For 3.2 mm thick plates, wave entrainment, air entrapment, and splashing are all more pronounced on the left side than on the right. Air entrapment occurs due to excessive inlet flow speed, leading to flow front instability. Mechanical properties on the left side are inferior to those on the right.
For 4.5 mm thick plates, the proportion of air entrapment and splashing is higher on the right side than on the left. Although wave entrainment is slightly greater on the left, the difference is not significant. Mechanical properties on the left side surpass those on the right.
For 6.5 mm thick plates, the proportion of air entrapment, wave entrainment, and splashing is higher on the right side than on the left. Due to greater thickness, the internal filling process is slower and more stable, while the outer side provides more space for wave entrainment. Mechanical properties on the left side exceed those on the right.
During the filling process, plates located on the outer side exhibit higher inlet flow speeds than those on the inner side. The inlet speed affects the splashing ratio during mold filling. Splashing is highly unstable and often results in incomplete filling, causing air entrapment in the molten aluminum or rapid backflow to the tail end of the specimen, leading to significant air entrapment and increased oxide film and inclusion proportions.
Keywords: A356 aluminum alloy, low-pressure casting, oxide film, numerical simulation, mechanical properties
The experiments reveal that thicker cast specimens exhibit better mechanical properties due to sufficient holding pressure and time, which ensure complete filling and refinement of dendritic arm spacing. Conversely, for 2.8 mm thick plates, excessive pressure during mold filling causes unstable flow at the rear end of the aluminum liquid, resulting in wall impact, turbulence, and entrainment of air into the molten aluminum. This leads to the formation of excessive oxide films in the central section of the specimens, adversely affecting their mechanical properties.
For 2.8 mm thick plates in low-pressure casting:
The proportions of turbulence and splashing are greater on the left side than on the right.
Air entrainment forms at the mold entry point and propagates throughout the specimen with the molten aluminum′s flow, causing the left side to exhibit inferior mechanical properties compared to the right.
For 3.2 mm thick plates in low-pressure casting:
The proportions of air entrainment, turbulence, and splashing are also greater on the left side than on the right.
Air entrainment results from excessive flow speed at the mold entry, leading to instability in the flow front, causing the left side′s mechanical properties to be inferior to the right.
For 4.5 mm thick plates in low-pressure casting:
Air entrainment and splashing proportions are greater on the right side than on the left.
Although turbulence is slightly higher on the left side, the difference is not significant, and the left side exhibits superior mechanical properties compared to the right.
For 6.5 mm thick plates in low-pressure casting:
The proportions of air entrainment, turbulence, and splashing are all higher on the right side than on the left.
Due to the greater thickness, the flow speed during inner filling is slower and more stable, while the outer region experiences more turbulence due to the increased space, resulting in the left side having better mechanical properties than the right.
During the filling process, the outer plates have a higher mold entry speed than the inner plates. This entry speed influences the proportion of splashing during mold filling. Splashing is a highly unstable surface flow phenomenon, where the flow front may advance without complete filling, leading to air entrainment in the molten aluminum or backflow at the specimen′s rear end. This generates a large amount of air entrainment, significantly increasing the proportion of inclusions and oxide films. | en_US |