Semi-solid die casting and ordinary die casting are two core technologies in metal forming, each optimized for different production needs. While both inject metal into molds to create parts, their fundamental differences in metal state, process control, and performance make them suited for distinct applications—from high-strength automotive components to low-cost consumer goods. But what exactly sets them apart? How do these differences impact cost, efficiency, and part quality? And how do you choose the right technology for your project? This article answers these questions with detailed comparisons and actionable insights.
1. Core Definitions & Principles: The Fundamental Gap
The biggest difference between the two technologies lies in the state of the metal during processing, which shapes their entire working mechanisms.
A. Ordinary Die Casting
- Metal State: Uses fully molten liquid metal (e.g., aluminum alloy heated to ≥650°C). The metal flows like water, with low viscosity and Newtonian fluid characteristics.
- Core Mechanism: Relies on high speed and high pressure (typical pressure: 100–150MPa) to force liquid metal to fill complex mold cavities quickly (often in <0.1 seconds). Rapid cooling in the mold then solidifies the metal into the desired shape.
- Microstructure Result: Due to fast cooling, the final part has fine but unevenly distributed grains, plus a large number of eutectic structures. This often leads to defects like shrinkage holes and stomata (porosity), especially in thick-walled areas.
B. Semi-Solid Die Casting
- Metal State: Uses semi-solid slurry or billets—a solid-liquid coexistence state (solid fraction: 50–90%). The metal behaves like “toothpaste”: thick, viscous, and non-Newtonian (its flowability improves with shear force).
- Core Mechanism: Leverages the high viscosity and non-dendritic microstructure of semi-solid metal. It fills the mold at a slower, more controlled speed (no turbulent splashing), reducing gas entrainment and defect risks.
- Microstructure Result: Spherical primary solid phase particles are evenly distributed in the liquid phase. After solidification, the part has fine spherical grains and a fibrous matrix, leading to better mechanical property uniformity (isotropy) and fewer defects.
2. Side-by-Side Process Comparison: Key Operational Differences
To understand how these technologies perform in practice, let’s compare their process steps, parameters, and constraints in a clear table:
| Process Aspect | Ordinary Die Casting | Semi-Solid Die Casting |
| Metal Pretreatment | Simple: Melt metal directly to a liquid state; no special preparation. | Complex: Requires semi-solid slurry/billet production (via mechanical mixing, electromagnetic stirring, or low-temperature deposition). |
| Filling Characteristics | High-speed jetting (often >5m/s); prone to eddy currents and metal splashing. | Slow, smooth filling (typically <2m/s); high viscosity prevents turbulence. |
| Typical Operating Pressure | 100–150MPa (needs high pressure to overcome liquid metal inertia). | 60–100MPa (lower pressure due to reduced flow resistance of semi-solid metal). |
| Mold Heat Load | Extremely high (liquid metal releases large latent heat); requires a powerful cooling system (e.g., water channels every 20mm). | Low (semi-solid metal has less latent heat to release); cooling system can be simpler. |
| Solidification Shrinkage | Large (liquid metal contracts significantly during cooling); easy to form shrinkage defects. | Smaller (solid phase already dominates the metal, reducing total contraction). |
| Minimum Wall Thickness | Capable of ultra-thin walls (down to 0.5mm); ideal for lightweight parts. | Limited (typical minimum: ≥1mm); semi-solid metal’s viscosity struggles to fill tiny gaps. |
| Cycle Time | Extremely fast (<30 seconds per part); no extra steps for slurry preparation. | Longer (45–90 seconds per part); includes time for slurry production or billet reheating. |
3. Performance & Application: Which Shines Where?
The process differences directly translate to distinct performance advantages—making each technology better suited for specific part types.
A. Performance Comparison
| Performance Metric | Ordinary Die Casting | Semi-Solid Die Casting |
| Tensile Strength | Lower (e.g., 200–250MPa for aluminum alloys). | Higher (15–30% increase; e.g., 230–325MPa for aluminum alloys). |
| Elongation | Low (typically 2–5% for aluminum parts). | Doubled (4–10% for aluminum parts); spherical grains hinder crack propagation. |
| Defect Rate | High (porosity and shrinkage are common; scrap rate: 5–12%). | Low (greatly reduces stomata and shrinkage; scrap rate: 1–3%). |
| Heat Treatment Stability | Poor (heat treatment often expands existing pores, causing deformation). | Excellent (uniform microstructure resists deformation; suitable for T6 heat treatment). |
| Cost per Part | Low (\(0.3–\)1 per kg for aluminum parts); mature equipment and simple process. | High (\(0.8–\)2 per kg for aluminum parts); needs special slurry equipment. |
B. Application Scenarios: Choosing the Right Fit
The table below maps each technology to its ideal use cases, based on performance and cost needs:
| Part Requirement | Prefer Semi-Solid Die Casting | Prefer Ordinary Die Casting |
| Safety-Critical Parts | Automotive steering knuckles, brake calipers (need high strength and low defects). | None—safety parts require reliability beyond ordinary die casting’s capabilities. |
| Pressure-Resistant Components | Hydraulic valve bodies, air compressor cylinders (no pores to leak under pressure). | Small electrical enclosures (no pressure load; cost is key). |
| High-Toughness Needs | Motorcycle hubs, golf heads (must withstand impact without cracking). | Toy models, simple brackets (low impact risk). |
| High-Temperature Service | Engine head brackets (stable microstructure resists heat deformation). | Cookware handles (low heat exposure; cost matters more). |
| Ultra-Thin or High-Volume Parts | None—struggles with thin walls and slow cycle times. | Home appliance shells, lamp frames, consumer electronics casings (high volume, low cost). |
4. Equipment & Cost: The Investment Tradeoff
Choosing between the two technologies also means evaluating upfront and long-term costs, driven by equipment differences.
A. Equipment Requirements
| Equipment Type | Ordinary Die Casting | Semi-Solid Die Casting |
| Core Machine | Standard die casting machine (e.g., 200–300-ton models); widely available. | Specialized machine with slurry feeding systems; often custom-built. |
| Pretreatment Gear | Basic melting furnace (no extra tools needed). | Slurry preparation equipment (e.g., electromagnetic stirrers, low-temperature deposition units). |
| Mold Design | Simple molds (focus on fast cooling; no special flow controls). | Molds with optimized gating (to handle viscous semi-solid metal; may need larger runners). |
B. Cost Breakdown (Aluminum Alloy Parts, 10,000-Part Batch)
| Cost Category | Ordinary Die Casting | Semi-Solid Die Casting |
| Equipment Investment | \(50,000–\)100,000 (standard machine + furnace). | \(150,000–\)300,000 (specialized machine + slurry gear). |
| Mold Cost | \(5,000–\)15,000 (simple design, no complex features). | \(10,000–\)25,000 (optimized for semi-solid flow). |
| Per-Part Material Cost | \(0.3–\)0.5 (higher waste rate: 10–15% due to defects). | \(0.4–\)0.6 (lower waste rate: 3–5% fewer defects). |
| Total Batch Cost | ~\(8,000–\)17,500 | ~\(25,000–\)51,000 |
5. Technological Evolution: Future Trends
Both technologies are evolving to address their limitations—with semi-solid casting leading in innovation for high-performance needs.
A. Semi-Solid Die Casting Innovations
- Intelligent Slurry Control: Real-time electromagnetic stirring devices now monitor and adjust the solid fraction (to ±2%) during slurry production, ensuring consistent metal quality.
- Composite Molding: Combining semi-solid casting with squeeze casting further increases part density (reducing remaining porosity to <0.5%).
- New Material Adaptation: Expanding to magnesium alloys (lighter than aluminum) and high-entropy alloys (superior heat resistance), opening doors for aerospace applications.
- Green Manufacturing: Uses ~20% less energy than ordinary die casting (no need to fully melt metal), aligning with sustainability goals.
B. Ordinary Die Casting Improvements
- Defect Reduction: Adding vacuum systems to remove gas during filling reduces porosity by 30–40%.
- Automation: Fully automated lines (with robotic part removal) cut labor costs by 50% and boost cycle time consistency.
6. Yigu Technology’s Perspective on the Two Technologies
At Yigu Technology, we see semi-solid and ordinary die casting as complementary tools—not competitors. For automotive clients needing safety parts (e.g., brake calipers), our semi-solid die casting solutions (equipped with real-time slurry monitoring) deliver tensile strength gains of 25% and scrap rates below 2%, meeting IATF 16949 standards. For consumer electronics clients, our optimized ordinary die casting lines (with vacuum degassing) reduce costs by 30% while keeping defects low enough for non-load parts.
We’re investing in “hybrid manufacturing” models: using semi-solid casting for high-strength main structures and ordinary casting for secondary features (e.g., integrated die-cast automotive bodies). This balances performance and cost, helping clients avoid overpaying for technology they don’t need. Our goal is to tailor each solution to the part’s actual requirements—no one-size-fits-all.
FAQ
- Can semi-solid die casting be used for ultra-thin parts (e.g., 0.5mm walls)?
No—semi-solid metal’s high viscosity makes it hard to fill tiny gaps. Ultra-thin parts (≤0.8mm) are better suited for ordinary die casting, which uses low-viscosity liquid metal to reach narrow cavities. For parts with mixed thicknesses (e.g., a 1mm main body + 0.6mm ribs), consider hybrid designs: use semi-solid casting for the main body and post-machine the thin ribs.
- Is semi-solid die casting worth the higher cost for non-safety parts?
It depends on the part’s function. If the part needs to withstand impact, pressure, or heat (e.g., hydraulic fittings), yes—semi-solid casting’s durability reduces long-term maintenance costs. If it’s a non-load decorative part (e.g., lamp shades), ordinary die casting is more cost-effective. We recommend calculating the “total cost of ownership” (not just per-part cost) to decide.
- Can ordinary die casting parts be heat-treated to match semi-solid casting performance?
Rarely—ordinary die casting parts have hidden pores and uneven microstructures. Heat treatment (e.g., T6) often expands these pores, causing deformation or even cracking. Semi-solid casting parts, with their uniform spherical grains, can handle heat treatment without issues, but ordinary parts typically cannot achieve the same strength gains. For heat-treated parts, semi-solid casting is the more reliable choice.