Special Alloys Forging Process: Challenges & Recommendations

The process of forging special alloys exhibits both common and unique traits. It is crucial to develop reasonable forging process specifications and choose suitable equipment based on the characteristics of different alloy materials. This article explores the forging characteristics of several commonly used special alloys, including high-temperature alloys, titanium alloys, stainless steel, aluminum alloys, magnesium alloys, and copper alloys. For each alloy, we will summarize the relevant forging considerations and process recommendations to help manufacturers optimize their production processes.

High-Temperature Alloys

High-temperature alloys are widely used in aerospace, energy, and chemical industries due to their excellent performance in extreme environments. However, forging these alloys presents various challenges.

1. Characteristics

Low Workability: These materials exhibit low plasticity at high temperatures, making deformation difficult and requiring greater pressure during forging.
High Resistance to Deformation: The high resistance encountered during deformation increases the load on forging equipment and may lead to early wear of molds.

Narrow Deformation Temperature Range: There is a limited range of suitable deformation temperatures, necessitating precise temperature control to ensure forging quality.

2. Forging Process Recommendations

Heat Treatment: The grain structure of high-temperature alloys cannot be refined through heat treatment; thus, optimizing forging parameters is essential to control grain size and microstructure.

Heating Method: Using a neutral atmosphere for heating is recommended to prevent oxidation and loss of alloying elements, ensuring stable material composition.

Lubrication Application: It is advisable to use glass protection lubricants on the workpiece to reduce temperature drop on the alloy surface during forging, decrease deformation resistance, and improve plasticity.

Titanium Alloys

Titanium alloys are known for their excellent strength-to-weight ratio, good corrosion resistance, and high-temperature performance, making them popular in aerospace, military, medical, and chemical applications. However, forging titanium alloys presents unique challenges and requirements.

1. Characteristics

Chemical Reactivity: Titanium alloys can easily absorb hydrogen and oxygen, leading to surface embrittlement and significantly reduced plasticity and workability.

Strong Adhesion: Fresh metallic surfaces tend to adhere to mold surfaces during forging, potentially causing damage to both molds and workpieces.

2. Forging Process Recommendations

Lubricant Use: Workpieces for die forging must be coated with glass protection lubricants to reduce friction, lower forging pressure, and prevent adhesion between the workpiece and mold.

Atmosphere Control: Processing in a neutral or slightly oxidizing atmosphere is crucial to reduce harmful gas absorption and the formation of surface embrittlement layers, thus maintaining workpiece performance.

Heating Control: Slow heating of the workpiece is necessary to avoid thermal stress concentrations and embrittlement, ensuring the material's workability.

Stainless Steel

Stainless steel is widely used in construction, chemicals, food processing, and medical equipment due to its excellent corrosion resistance and strength. Its forging performance is influenced by factors such as alloy composition, microstructure, and processing conditions.

1. Characteristics

Duplex Stainless Steel: This type has high resistance to deformation and a relatively narrow deformation temperature range, limiting processing flexibility.

Single-Phase Stainless Steel: It cannot be adjusted through heat treatment, increasing the complexity and technical requirements of forging.

2. Forging Process Recommendations

Temperature Control: Strictly controlling the deformation temperature is essential to optimize plasticity and toughness during the forging process and ensure stable microstructure.

Process Parameter Adjustment: Tailoring process parameters for different types of stainless steel, along with appropriate heating and forging methods, can enhance forging efficiency and quality.

Aluminum Alloys

Aluminum alloys are valued for their lightweight, high strength, and good formability, making them widely used in aerospace, automotive, construction, and electronics. However, forging aluminum alloys has specific characteristics and requirements.

1. Characteristics

Narrow Deformation Temperature Range: Typically between 100°C and 150°C, this limits processing flexibility.

Sensitivity to Strain Rate: Aluminum alloys are sensitive to deformation rates, with rapid deformation potentially leading to cracking or failure.

2. Forging Process Recommendations

Uniform Heating: Using electric furnaces with forced air circulation ensures even temperature distribution, controlled within ±5°C to prevent material property degradation due to localized overheating.

Equipment Selection: For large aluminum alloy die forgings, hydraulic presses are recommended, while medium and small forgings can use mechanical or screw presses. Hammers should be avoided to reduce the risk of uneven stress on the material.

Magnesium Alloys

Magnesium alloys are increasingly recognized for their lightweight, high strength, and good corrosion resistance, making them important materials in aerospace, automotive, and electronics. However, magnesium alloys present unique challenges in their forging processes.

1. Characteristics

Narrow Deformation Temperature Range: Typically between 70°C and 150°C, this limits processing flexibility and adaptability.
High Thermoplasticity: They exhibit good thermoplasticity at low speeds, making them suitable for forging.

2. Forging Process Recommendations

Temperature Control: Uniform heating in electric furnaces with forced air circulation should be maintained within ±5°C to avoid quality issues caused by temperature fluctuations.

Forging Method: Hydraulic presses are recommended for forging to minimize crack risks. Mechanical or screw presses can also be used, but hammer die forging is not advised to reduce the likelihood of brittle failure.

Copper Alloys

Copper alloys are widely used in electrical, electronic, construction, and machinery manufacturing industries due to their excellent electrical conductivity, thermal conductivity, and corrosion resistance. Despite their outstanding performance, copper alloys face specific challenges and requirements in forging.

1. Characteristics

High Plasticity and Good Flowability: They are suitable for various forging techniques, especially extrusion, but can also be die-forged.

Homogenization Annealing Requirements: Large copper alloy ingots require homogenization annealing to eliminate internal stresses and improve plasticity and ductility.

2. Forging Process Recommendations

Atmosphere Control: Heating should occur in a neutral or slightly oxidizing atmosphere to prevent hydrogen embrittlement, ensuring the quality of copper alloys.

Forging Temperature: The final forging temperature should be above the brittle temperature zone, and forging should stop above 650°C to prevent significant degradation of material properties.

Conclusion

In summary, each type of special alloy exhibits distinct characteristics during the forging process. Understanding these differences and developing targeted process flows and equipment choices can enhance production efficiency and ensure the quality and stability of forged components. Through scientifically sound forging practices, manufacturers can fully leverage the superior properties of special alloys to meet various high-end application needs. As we look to the future, manufacturers should continuously monitor advancements in new material technologies and forging processes to adapt to increasingly complex market demands and enhance their competitiveness.