| 摘要: | 本研究以A356(Al-Si-Mg)之鋁合金進行不同厚度鑄件低壓鑄造實驗，實驗目的為經由本實驗探索不同厚度之試片鋁合金於實務鑄造上的流動填充與氧化膜生成的條件與方式，透過調整鑄造參數如低壓鑄造壓力、加壓時間、模具預熱溫度等來探討填充流動波前問題，並輔以MAGMA5.5模擬軟體互相驗證分析。
實驗得知鑄件試片越厚，其機械性質較佳，原因為保壓時間與壓力充足得到完整的填充與樹狀晶枝狀間距得到補充。相對來說厚度2.8 mm的板件會因鋁湯充模時壓力過大導致尾端鋁湯流動不穩定介面撞擊模壁造成浪捲、捲氣，將其帶進鋁液內部並向中間段補充，導致過多的氧化膜在試棒中間段產生使得機械性質不佳。
1.低壓鑄造鋁合金薄板厚度2.8mm的板件在浪捲與噴濺的比例是左側大於右側，容易在入模口處形成了捲氣，並隨著熔融鋁合金的補充推進，使得此捲氣泡流經整個試片，機械性質左小於右。
2.低壓鑄造鋁合金薄板厚度3.2mm的板件在捲氣、浪捲與噴濺的比例都是左側大於右側，捲氣為入模流速過快導致波前與實際補充流動產生，機械性質左小於右。
3.低壓鑄造鋁合金薄板厚度4.5mm的板件在捲氣與噴濺的比例是右側大於左側，浪捲雖然左側較大於右側，但是並不存在明顯的差異，機械性質左大於右。
4.低壓鑄造鋁合金薄板厚度6.5mm的板件在捲氣、浪捲與噴濺的比例皆是右側大於左側，因為其厚度較大，其在內側時補充時的速度也較慢與穩定，但在外側時也會賦予他更多的空間浪捲，機械性質左大於右。
在填充過程中，位在外側的板件入模速度大於位在內側的板件，入模速度影響了鋁湯充模噴濺的比例，噴濺屬於極為不穩定的液面流動，很容易波前先行通過卻並未完整填充，導致熔融鋁合金中間產生捲氣，或是過快的流至試片尾端回流，產生大量的捲氣，使得介在物與氧化模的比例大增。
;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. |
