Selection of Tool Steel for Aluminum Extrusion Dies
Aluminum extrusion is a high-pressure forming process in which heated billets (typically 340–510°C) are forced through a die. During operation, the die is subjected to sustained compressive stress, often reaching 1035 MPa (150 ksi), combined with continuous thermal exposure.
Because extrusion is typically performed without lubrication, aluminum tends to adhere to the die surface, increasing friction and shear stress at the interface. In service, die failure is mainly driven by three mechanisms: abrasive wear from metal flow, adhesive wear due to sticking, and thermal fatigue (heat checking). Heat checking appears as a network of surface cracks caused by repeated heating and cooling, and is often the dominant factor limiting die life.
Selection Factors
Tool steel selection should be based on resistance to the actual failure modes observed in extrusion service.
Hot Hardness (Tempering Resistance)
Insufficient hot hardness leads to softening and plastic deformation under load, resulting in profile distortion and accelerated wear during long extrusion runs.
Toughness
Cracking risk increases under high stress, especially in large dies, complex geometries, or unstable extrusion conditions. Higher toughness reduces the likelihood of gross cracking and premature failure.
Wear Resistance
Adhesion and sliding between aluminum and the die surface cause continuous material loss. Increasing hardness improves wear resistance, but reduces toughness, making edge cracking more likely.
Resistance to Heat Checking
Thermal fatigue resistance determines how well the die withstands cyclic expansion and contraction. Poor resistance leads to surface crack networks that propagate, shortening die life.
Recommended Tool Steels
Typical working hardness: 42–50 HRC. Differences in performance are determined by composition and carbide structure.
AISI H11 Tool Steel | 1.2343 | SKD6
H11 is a 5% chromium hot-work tool steel with relatively low vanadium content, resulting in lower carbide volume and higher toughness.
It is selected when cracking is the primary failure risk, such as in large dies, thick sections, or applications with high mechanical shock. Compared to H13, it offers better resistance to thermal shock but lower wear resistance.
H13 Tool Steel Supplier | 1.2344 | SKD61
H13 contains approximately 1.0% vanadium, forming stable carbides that improve wear resistance.
It is the standard choice for aluminum extrusion dies where a balance of wear resistance and toughness is required. In most general extrusion applications, H13 provides sufficient resistance to both wear and cracking. Nitriding is commonly applied to improve surface hardness and reduce adhesive wear without sacrificing core toughness.
AISI H12
H12 contains tungsten, which improves resistance to softening at elevated temperatures.
It is used when dies are subjected to prolonged thermal exposure and require greater deformation resistance than H11 while still maintaining reasonable toughness. It is suitable for long production cycles in which softening, rather than cracking, limits die life.
Summary Comparison Table
| Tool Steel Grade | Key Characteristics | Primary Advantage |
| AISI H11 | 5% Cr, low V | Best resistance to cracking and thermal shock |
| AISI H12 | 5% Cr, W-alloyed | Better resistance to high-temperature softening |
| AISI H13 | 5% Cr, ~1.0% V | Balanced wear resistance and toughness; suitable for nitriding |