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Forging of Aluminum Alloys

Forging process is the common metal working process in production. It mainly takes advantage of the plasticity of materials and causes plastic deformation of materials with the help of external forces, so as to obtain required shapes, sizes and certain performances. As far as the forging process itself is concerned, the advantage is that the inside of the forging is compact, the structure is relatively uniform, and there are no pores in the interior. The drawback is that larger deformation forces are required. According to the placement of tools and molds, forging can be divided into open die forging, closed die forging and roll forging. Open die forging is formed by a fixed flat anvil, the forging die of roll forging is mobile, and the forging die of closed die forging is fixed. According to the forging temperature, forging can be divided into hot forging, cold forging and warm forging. Aluminum and aluminum alloy are the most widely used nonferrous metals, with the yield second only to that of steel. Some key processes in aluminum alloy forging are introduced below.

forging of aluminum alloys

Forging Blanking
. Excessive aluminum materials cause waste and aggravate bore wear and energy loss; otherwise, too little materials will increase the adjustment difficulty of forging process and increase the reject rate. The so-called blanking is cutting raw materials into the desired length of blanking before forging, which can be achieved by cutting machine, press and other equipment.

Forging. Lubrication is needed in forging to improve aluminum mobility and reduce surface defects. Water base graphite is often used as lubricant in warm forging, and no lubricant is used in cold forging. Aluminum alloy is most suitable for forging on low-speed pressure machine. Due to its high external friction coefficient and poor fluidity, it is easy to cause various defects in the forging if the deformation is too fast. At the same time, the parting surface should be reasonably selected. If the selection of parting surface is not reasonable, it will eventually reduce the fatigue strength and corrosion resistance of the aluminum forging.

T4+T6 Heat Treatment. The process is a combination of quenching and artificial aging, aiming to improve the strength and ensure good comprehensive performance of forgings in aluminum alloy. However, for aluminum alloy that cannot be heat treated and strengthened, it can only be annealed. For aluminum alloy that can be heat treated and strengthened, quenching aging is the final form of heat treatment.

Trimming and Punching. Trimming and punching hole can be divided into hot or cold trimming, and hot or cold punching. Among them, hot punching and cold punching are carried out immediately after closed die forging, while hot trimming and cold trimming are carried out after the forging is cooled at room temperature. In addition to superhard aluminum, if the size of the forging is not large, generally under the cold cutting.

Surface Finishing. Surface treatment mainly includes rough vibration, polishing and fine vibration, and its purpose is to remove burrs, rounding angles, bright polishing and remove parting lines.Rough vibration adopts vibrator, which generally takes 2.5 hours. Fine vibration also adopts vibrator, but it only takes about half an hour to polish. Grinding using nylon wheel, need to pay attention to the size of the grinding degree.

Aluminum alloy can be used in the manufacturing of mechanical parts or components which bear large loads and become widely used non-ferrous metal materials in the industry. Due to its high specific strength and light weight, aluminum alloy becomes the main structural material of aerospace forgings. As a common metal material in daily forging production, the application of aluminum alloy is far more than that. More applications and improvements of aluminum forgings need to be found.

Four Types of Defects Caused by Improper Forging of Aluminum Alloys

1. Coarse grain

Caused by excessive initial forging temperature and insufficient deformation degree, or excessive final forging temperature, or deformation degree falling to critical deformation area.The deformation degree of aluminum alloy forging is too large, forming texture. Superalloy deformation temperature is too low, which may cause coarse grain when forming mixed deformation structure.

The coarse grain will reduce the plasticity and toughness of the alumimum forgings, and the fatigue property will also decrease obviously. Unevenness of grain: refers to some areas of the grain in the forging is particularly thick and large, but quite small in some areas. The main reason for the unevenness of grain is that the deformation of the billet is not uniform and the degree of grain crushing is not consistent, or the deformation degree of local area falls into the critical deformation area, or coarse grains during quenching and heating.The unevenness of grain will decrease the durability and fatigue of aluminum forgings.

2. Cold Hardening

During the deformation, due to the low temperature or too fast deformation rate, as well as the rapid cooling after forging, the softening caused by recrystallization can not keep up with the strengthening caused by deformation (hardening), so the cold deformation structure is still partially retained inside the forgings after hot forging. The existence of this tissue improves the strength and hardness of the forging but reduces plasticity and toughness. Severe cold hardening can cause cracking.

3. Crack

The crack is usually caused by large tensile stress, shear stress or tensile stress in aluminum alloy forging. The place where the crack occurs is usually in the place where the stress and thickness of the blank is the greatest.If there are microcracks on the surface and inside of the blank, or there are defects in the structure inside the blank, or the improper thermal processing temperature reduces the plasticity of the material, or the deformation speed is too fast, the deformation degree is too large, beyond the allowable plastic pointer of the material, etc., then, cracks may be generated in the process of upseting, drawing the length, punching the hole, expanding the hole, bending and extrusion.

4. Fracturing

Fracturing is the turtle shape crack that exsits on the surface of the forging. This defect is most likely to occur on surfaces that are subjected to tensile stress during forging (for example, unfilled protrusions or curved parts).The internal cause of fracturing may be various: overabundance of fusion elements such as Cu, Sn, etc. 

Contact CFS Drop Forging If you have any RFQs of aluminum forgings.

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