Core Purposes and Application Value of Post-Casting Heat Treatment

Post-casting heat treatment constitutes an indispensable phase in the foundry production process, with its fundamental objective centered on comprehensively enhancing the integrated performance and service reliability of castings through precise regulation of internal microstructure and stress states. Its principal goals can be categorized into four key areas:

1. Eliminating Residual Stress and Stabilizing Dimensions

Residual stress resulting from uneven cooling or complex geometries during casting is the primary cause of deformation or cracking. Through annealing or stress-relief annealing (heating to 280–300°C followed by slow cooling), both casting stress and machining-induced stress can be effectively eliminated. This process additionally stabilizes α-solid-solution structures, inhibits volumetric changes during service, and ensures long-term dimensional stability—particularly crucial for precision instrument components.

2. Enhancing Mechanical Properties and Microstructure Optimization

Heat treatment significantly improves mechanical characteristics:

Strengthening Hardness and Strength: Solution treatment (quenching) dissolves strengthening phases and rapidly fixes them; subsequent aging precipitates dispersed hardening phases (e.g., G-P zones), substantially increasing tensile strength and hardness.

Refining Grains and Homogenization: Normalizing or cyclic treatments refine coarse as-cast structures, eliminate compositional segregation, and enhance toughness and fatigue resistance. For instance, aluminum alloys subjected to T6 treatment (solution treatment + full artificial aging) exhibit ≈30% strength improvement.

3. Improving Machinability and Process Adaptability

Annealing facilitates spheroidization of plate-like silicon in Al-Si alloys, enhancing ductility and machinability. Quenching and tempering balance strength with toughness, optimizing subsequent welding or forging capabilities. These processes improve a casting’s adaptability to complex machining requirements, thereby reducing production costs.

4. Mitigating Internal Defects and Extending Service Life

Heat treatment reduces the adverse effects of casting defects: high-temperature diffusion heals gas pores and shrinkage cavities, while stabilization tempering (T7 treatment) or overaging enhances corrosion resistance and stress-cracking resistance. For example, titanium alloys demonstrate significantly prolonged fatigue life after decoating and step aging.