I. Core Material Properties and Die-casting Compatibility
Precision steel die-castings
Material property
The base material is mainly carbon steel (such as Q235, 45# steel) and alloy steel (such as 304 stainless steel, 1Cr13), with a carbon content of 0.1%-1.5%, a density of 7.85g/cm³, a tensile strength of 500-1500MPa, high temperature resistance (above 450℃), and excellent wear resistance.
Difficulties in die casting: High melting point (1400-1538℃), poor fluidity, and the need to use a cold chamber die casting machine (injection pressure 100-200MPa). The mold material should be hot work die steel such as H13 and 8407 (hardness HRC48-52) to avoid mold sticking and thermal fatigue.
Typical process: The mold preheating temperature is 200-300℃, the pouring temperature is 1550-1650℃, vacuum die-casting is used to reduce porosity, and subsequent annealing (to eliminate internal stress) or surface hardening (to enhance hardness) is required.
Application scenarios
High-strength structural components: automotive transmission housing, gearboxes (capable of withstanding high loads), industrial valves (resistant to high pressure).
Wear-resistant components: hydraulic
Valve blocks for construction machinery, gears for mining machinery (surface carburizing treatment is required).
Disadvantages: High production cost (mold life is only 50,000 to 100,000 times), yield of finished products is about 80% to 85%, and subsequent machining is required to remove the gate and flash.
2. Cast iron die-castings
Material property
Matrix: Gray cast iron (HT200, HT300, graphite in flake form), ductile iron (QT400-18, QT500-7, graphite in spherical form), carbon content 2.5%-4.0%, density 7.2-7.3g/cm³, tensile strength 200-700MPa, excellent shock absorption (damping is 10 times higher than that of steel) However, it has relatively low toughness (strong notch sensitivity).
Advantages of die casting: Good fluidity in the molten state (carbon exists in the form of graphite, reducing the melting point to 1150-1250℃), capable of forming complex thin-walled parts (wall thickness ≥3mm), mold life of 100,000 to 200,000 times (higher than steel die casting).
Key points of the process: The cooling rate needs to be controlled (to avoid white cast iron structure), and semi-solid die casting or extrusion die casting is commonly used to reduce shrinkage cavities. The surface can be treated with phosphating and spraying.
Application scenarios
Shock-absorbing and wear-resistant parts: Automotive engine block (utilizing the shock-absorbing property of gray cast iron), machine tool base (resistant to deformation), water pump casing (with better corrosion resistance than steel).
Disadvantages: High density (2.5 times heavier than aluminium), not suitable for lightweight scenarios; It has poor toughness and is prone to breakage under impact.
3. Aluminum die-castings
Material property
Matrix: The commonly used aluminum alloys are ADC12 (Japanese standard, Si content 11%-13%), A380 (American standard, Si8.5%-10.5%, Fe≤1.3%), and 6061 (heat-treatable and strengthened, containing Mg1.0%-1.5%), with a density of 2.7g/cm³ and a tensile strength of 200-400MPa. It has excellent thermal conductivity (180-200W/(m · K)) and is easy to surface treat.
Advantages of die casting: Low melting point (660℃), suitable for hot chamber die casting machines (small parts) or cold chamber die casting machines (large parts), injection pressure 50-100MPa, mold life 500,000 to 1,000,000 times (aluminum alloy causes less erosion to the mold), and the yield rate can reach over 90%.
Process extension: Strength can be enhanced through T4 (solution treatment + natural aging) and T6 (solution treatment + artificial aging) heat treatment, surface anodizing (thickness 5-25μm), and electrophoretic painting (salt spray resistance for over 500 hours).
Application scenarios
Lightweight components: Automotive engine cylinder heads (30% weight reduction), wheels (A356 aluminum alloy), 3C product casings (such as mobile phone frames, which require heat conduction and electromagnetic shielding).
Heat dissipation components: LED lamp heat sink (utilizing high thermal conductivity), new energy vehicle battery shell (requiring a balance between lightweight and strength).
Disadvantages: Poor high-temperature resistance (strength drops significantly above 200℃), prone to intergranular corrosion (the content of Fe and Cu elements needs to be controlled).
