In forging production, in addition to the shape and size required by forging, the performance requirements of parts in use must also be met, including strength indicator, plasticity indicator, impact toughness, fatigue strength, fracture toughness and stress corrosion resistance. For aluminum alloy parts working at high temperature, there are also high-temperature instantaneous tensile properties, creep resistance and thermal fatigue properties. The raw materials for forging are steel ingot, rolled product, extruded product and forging blank. Rolled material, extruded material and forged blank are semi-finished products formed by rolling, extruding and forging steel ingots respectively.

In forging production, the structure and properties of raw materials can be improved by adopting reasonable technological process and technological parameters in the following aspects:

1. Break columnar crystals, improve macro segregation, change as-cast structure into as-forged structure, and weld internal pores under appropriate temperature and stress conditions to increase the density of materials;

2, the ingot is forged to form a fiber structure, and further through rolling, extrusion and die forging, the forging has a reasonable fiber direction distribution;

3, controlling the size and uniformity of crystal grains;

4. Reasonable distribution (for example, alloy carbide in steel);

5, make the organization have deformation strengthening or deformation-phase transformation strengthening, etc.

Due to the improvement of the above structure, the plasticity, impact toughness and fatigue strength of forging are also strengthened, and then the good comprehensive properties such as hardness, strength and plasticity required by the parts can be obtained through heat treatment.

However, if the quality of raw materials is poor or the forging process adopted is unreasonable, forging defects, including surface defects or unqualified performance, may occur.

Causes of folding and cracking of aluminum alloy precision forgings

Aluminum alloy precision forgings are widely used in parts with certain requirements for medium and high strength because of their small specific gravity, good thermal conductivity, high electrical conductivity and corrosion resistance. The technical characteristics of aluminum alloy heating die forgings are poor fluidity, low plasticity, good thermal conductivity, narrow forging temperature range, and strict requirements for initial forging and final forging temperatures. The performance characteristics of heating die forgings are that aluminum alloy does not produce allotropic transformation, and the metal structure is improved mainly by correctly controlling the mechanical parameters of forgings, so that metal streamline is evenly and continuously distributed along the shape of forgings to improve mechanical properties. The quality characteristic of heating die forging is that aluminum alloy is prone to two major quality defects: folding and cracking. Among them, folding will reduce the stress area of parts, and it is easy to produce stress concentration when in service, which becomes the source of fatigue failure and is very harmful. Folding waste accounts for about 70% ~ 80% of the total forging waste; Cracks are more harmful, and crack waste accounts for about 70% ~ 80%. It accounts for 5% ~ 10% of the total scrap steel of forgings.

The blanking size is φ50mm×55mm or 40mm×40mm×69mm, and the weight is 0.29kg. It will fold during forging. Macroscopically, it can be seen that the folding of the middle part is caused by the convection and convergence of two kinds of flowing metals, while the folding at the transition between φ23mm and the middle part is caused by local deformation. While one part of the metal is pressed into another part of the metal, the rapid flow of the metal brings the metal on the adjacent surface into the flow. In addition, there is some oxidation at the fold.

Causes of folding: large cross-sectional size of blank, unreasonable shape of blank, local press-forming, small radius of fillet at the transition of die cavity, and too much one-time reduction during operation.

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