Four Kinds of Aluminum Alloys Casting Material
(1) Al Si alloy
Also known as "Silicon Aluminum Ming" or "Silicon Aluminum Ming". It has good castability and wear resistance, and has a small coefficient of thermal expansion. It is the alloy with the most varieties and the largest amount among the cast aluminum alloys, with a silicon content of 10% - 25%. Sometimes 0.2% - 0.6% magnesium silicon aluminum alloy is added, which is widely used in structural parts, such as shell, cylinder block, box and frame. Sometimes adding an appropriate amount of copper and magnesium can improve the mechanical properties and heat resistance of the alloy. This kind of alloy is widely used in manufacturing piston and other parts.
(2) Aluminum copper alloy
The alloy containing 4.5% - 5.3% copper has the best strengthening effect. The appropriate addition of manganese and titanium can significantly improve the room temperature, high temperature strength and casting properties. It is mainly used to make sand castings that bear large dynamic and static loads and have uncomplicated shapes.
(3) Aluminum zinc alloy
In order to improve performance, silicon and magnesium are often added, which is often called "zinc silicon aluminum Ming". Under casting conditions, the alloy has quenching effect, namely "self quenching". It can be used without heat treatment, so the castings have higher strength after modification heat treatment. After stabilization, the size is stable, and it is often used to make models, plates and equipment supports.
(4) Aluminum magnesium alloy
The casting aluminum alloy with the lowest density (2.55g/cm3) and the highest strength (about 355MPa) contains 12% magnesium, and the strengthening effect is the best. The alloy has good corrosion resistance in the atmosphere and sea water, and has good comprehensive mechanical properties and machinability at room temperature. It can be used as radar base, engine case, propeller, landing gear and other parts of aircraft, as well as decorative materials.
Advantages and disadvantages of cast aluminum alloy
Advantages of cast aluminum alloy:
1. Good product quality:
The dimensional accuracy of castings is high, which is generally equivalent to grade 6-7, or even grade 4; Good surface finish, generally equivalent to grade 5~8; The strength and hardness are higher, and the strength is generally 25~30% higher than that of sand casting, but the elongation is reduced by about 70%; Stable size and good interchangeability; Die casting aluminum thin-walled complex castings. For example, at present, the minimum wall thickness of zinc alloy die-casting aluminum parts can reach 0.3mm; Aluminum alloy castings can reach 0.5mm; The minimum cast hole diameter is 0.7mm; The minimum pitch is 0.75mm.
2. High productivity:
The productivity of the machine is high. For example, the domestic J Ⅲ 3 horizontal cold air die casting aluminum machine can die cast aluminum 600 ~ 700 times per eight hours on average, and the small hot chamber die casting aluminum machine can die cast aluminum 3000 ~ 7000 times per eight hours on average; The service life of die-casting aluminum mold is long. A pair of die-casting aluminum mold and die-casting aluminum clock alloy can have a service life of hundreds of thousands or even millions of times; It is easy to realize mechanization and automation.
3. Good economic effect:
Due to the precise size of die-casting aluminum parts, the surface is bright and clean. Generally, it is no longer used directly for machining, or the processing volume is very small, so it not only improves the utilization rate of metal, but also reduces a lot of processing equipment and working hours; Castings are cheap; Composite die cast aluminum can be used with other metallic or non-metallic materials. It saves both assembly time and metal. Oxidation slag inclusion
Defects of cast aluminum alloy
1、 Oxidation slag inclusion
Defect characteristics:
Oxidation slag is mostly distributed on the upper surface of the casting, at the airtight corner of the mold. The fracture is mostly grayish white or yellow, which can be found by X-ray fluoroscopy or machining, or by alkaline washing, pickling or anodizing
2、 Blowhole bubble
Defect characteristics:
The pores in the wall of three castings are generally round or oval, with smooth surface, usually shiny oxide skin, and sometimes oil yellow. The surface pores and bubbles can be found by sandblasting, and the internal pores and bubbles can be found by X-ray fluoroscopy or machining. The pores and bubbles are black on the X-ray film.
3、 Shrinkage porosity
Defect characteristics:
Shrinkage porosity of aluminum castings generally occurs at the thick part of the riser root near the ingate, the thickness transition of the wall and the thin wall with a large plane. When as cast, the fracture is gray, light yellow. After heat treatment, it is gray white, light yellow or gray black. It is cloud like on the X-ray film. Serious filiform shrinkage can be found by X-ray, fluorescent low magnification fracture and other inspection methods.
4、 Crack
1. Casting cracks.
It develops along the grain boundary and is often accompanied by segregation. It is a kind of crack formed at higher temperature. It is easy to appear in alloys with large volume shrinkage and castings with complex shapes
2. Heat treatment cracks:
Due to over burning or overheating of heat treatment, it often presents transgranular cracks. It often cools too much in alloys with large stress and thermal expansion coefficient. Or other metallurgical defects
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