Aluminum is an active metal element, and aluminum easily oxidizes and absorbs the gas in the aluminum casting process. The aluminum oxidation (Al2O3) has a high melting point (2 050 ° C), the density slightly is greater than liquid aluminum. It is difficult to remove in the suspended liquid aluminum, and easy to form slag inclusions in the casting. During cooling, the gas in the molten aluminum is often blocked by the dense Al2O3 film. There are many pinholes in the casting, which affects the compactness and mechanical properties of the casting.
In order to avoid oxidation, fluxes with low melting points (such as NaCl, KCL, Na3 AIF6) are commonly used to isolate the liquid aluminum from the air. Minimize agitation as much as possible, and degas the aluminum liquid at the later stage of smelting. Refining is to pass chlorine gas into the aluminum liquid, or add hexachloroethane, zinc chloride to form bubbles, so that the hydrogen dissolved in the aluminum liquid enters the bubbles and precipitates. In the process of bubbles floating, the gas and Al2 03 inclusions in the aluminum liquid are taken out of the liquid surface, so that the aluminum liquid becomes pure.
Aluminum Casting Process
Cast aluminum alloy has a low melting point and is generally smelted in a crucible. Fine sand casting can reduce the surface roughness of the casting. In order to prevent the aluminum liquid from oxidizing and inhaling during the pouring process, an open pouring system is usually used, and open more inner runners. Straight runners are often snake-shaped or gooseneck-shaped, so that the alloy quickly and smoothly fills the cavity without splashing, vortex and impact. The aluminum alloy castings can adopt various casting methods.
Aluminum alloy smelting and pouring are the main links in casting production. Strictly controlling the whole process of melting and casting plays an important role in preventing casting defects. The aluminum melt has a strong tendency to absorb hydrogen, has a strong oxidizing ability, and easily dissolves iron. Simple and careful precautions must be taken during the melting and casting process to obtain high-quality castings.