Selecting the right metal for a manufactured part is one of the most consequential engineering decisions. It affects cost, performance, manufacturability, and product lifecycle. This guide covers the most widely used engineering metal categories with practical selection criteria.
Steel accounts for approximately 75% of all metal used in manufacturing globally. Its versatility comes from the wide range of alloying possibilities.
| Type | Carbon % | Characteristics | Common Applications |
|---|---|---|---|
| Low carbon (mild) | 0.05–0.25% | Soft, ductile, easily welded and machined; cannot be hardened by heat treatment | Automotive body panels, structural sections, pipes, general fabrication |
| Medium carbon | 0.25–0.60% | Balanced strength and ductility; heat-treatable (quench & temper) | Shafts, gears, axles, connecting rods, railway tracks |
| High carbon | 0.60–1.40% | High hardness, low ductility, excellent wear resistance | Cutting tools, springs, dies, knives, wear plates |
Chinese standard GB/T 13304 classifies alloy steels by total alloy content:
Stainless steel rule of thumb: Minimum 13% Cr provides basic corrosion resistance. 18% Cr + 8% Ni = 304 (the most common stainless grade). Adding 2% Mo = 316 (marine/chemical grade).
| Grade | Hardness (HRC) | Key Property | Application |
|---|---|---|---|
| H13 | 40–52 | Excellent hot hardness, thermal fatigue resistance | Die casting dies, hot forging dies, extrusion tooling |
| D2 | 58–62 | High wear resistance, good dimensional stability | Cold forming dies, blanking punches, shear blades |
| M2 | 62–65 | High-speed cutting capability, red hardness | Drills, end mills, taps, broaches |
| S7 | 48–56 | Excellent impact toughness, shock-resistant | Pneumatic tools, shear blades, forming tools |
| P20 | 28–35 | Good machinability, polishability | Plastic injection mold bases and cavities |
| NAK80 | 37–43 | Excellent polishability, pre-hardened | High-gloss plastic molds, texture-grade surfaces |
Aluminum's strength-to-weight ratio and corrosion resistance make it the second most widely used engineering metal. Wrought alloys are designated by a 4-digit system:
| Series | Main Alloy | Characteristics | Applications |
|---|---|---|---|
| 1xxx (99%+ pure) | None | Excellent corrosion resistance, electrical conductivity, very low strength | Electrical bus bars, chemical equipment, foil |
| 2xxx (Cu) | 2024 | High strength, poor corrosion resistance, heat-treatable | Aircraft structures (wings, fuselage) |
| 5xxx (Mg) | 5052, 5083 | Good weldability, moderate strength, marine-grade | Boat hulls, fuel tanks, pressure vessels |
| 6xxx (Mg+Si) | 6061, 6063 | Good extrudability, weldable, heat-treatable | Structural profiles, automotive parts, pipe/tube |
| 7xxx (Zn) | 7075 | Highest strength (approaches steel), difficult to weld | Aerospace, competitive sporting goods, tooling plates |
Casting alloys: A380 (general-purpose die casting), A356 (high-strength sand casting), ADC12 (Japanese standard, common in Asian die-casting).
Copper's excellent electrical and thermal conductivity make it irreplaceable in electrical and thermal management applications.
| Alloy | Composition | Key Properties | Applications |
|---|---|---|---|
| Pure copper (C110) | 99.9% Cu | 100% IACS conductivity, soft, difficult to machine | Electrical wire, bus bars, heat sinks |
| Brass (C360) | Cu-Zn-Pb | Free-machining, good corrosion resistance, decorative | Valves, fittings, plumbing, gears, decorative hardware |
| Bronze (C954) | Cu-Al-Fe | High strength, excellent wear resistance, corrosion resistant | Bearings, bushings, worm gears, marine propellers |
| Beryllium copper (C172) | Cu-Be-Co | Highest strength copper alloy, non-sparking, fatigue resistant | Mold cores, springs, electrical connectors, safety tools |
Titanium offers the highest strength-to-weight ratio among common engineering metals, combined with exceptional corrosion resistance.
| Grade | Description | Tensile Strength | Applications |
|---|---|---|---|
| Grade 2 (CP) | Commercially pure, good formability | 345 MPa | Chemical processing, heat exchangers |
| Grade 5 (Ti-6Al-4V) | Most common alloy, 90% of Ti usage | 900–1100 MPa | Aerospace, medical implants, high-end automotive |
| Grade 23 (Ti-6Al-4V ELI) | Extra low interstitial, improved fracture toughness | 860–1000 MPa | Surgical implants, cryogenic applications |
Key consideration: Titanium is expensive ($30–50/kg for Grade 5 sheet vs $0.40/kg for carbon steel) and difficult to machine (low thermal conductivity causes heat buildup at the cutting edge). It is used only where its weight/strength/corrosion advantage justifies the cost.
| Metal | Key Property | Application |
|---|---|---|
| Inconel (Ni-Cr superalloy) | Maintains strength at 700–1000°C | Gas turbine blades, exhaust systems, chemical reactors |
| Hastelloy (Ni-Mo-Cr) | Extreme corrosion resistance | Chemical processing equipment, pharmaceutical |
| Magnesium alloys | Lightest structural metal (1.74 g/cm³) | Aerospace brackets, laptop chassis, EV components |
| Tungsten carbide (WC-Co) | Extreme hardness (80–92 HRA) | Cutting tools, wear parts, mold cavities |
| Requirement | First Choice | Alternative |
|---|---|---|
| General structural (low cost) | Mild steel (Q235/A36) | 6061 aluminum (if weight matters) |
| High strength (not weight critical) | 4140 alloy steel (quench & tempered) | 7075 aluminum |
| Corrosion resistant (low cost) | 304 stainless steel | Aluminum 5052 |
| Corrosion resistant (marine) | 316 stainless steel | Titanium Grade 2 |
| High temperature (400–600°C) | H13 tool steel | Inconel 625 |
| Wear resistant (abrasive) | D2 tool steel | Tungsten carbide coating |
| Lightest weight | Magnesium AZ91 | Titanium Grade 5 (if stronger) |
| Electrical conductor | Copper C110 | Aluminum 1350 (if cost sensitive) |
| Heat conductor (heat sink) | Copper C110 | Aluminum 6061 (if lighter) |
| Food/pharma contact | 304 or 316 stainless | Titanium (if more aggressive cleaning) |
| Metal | Density (g/cm³) | Yield Strength (MPa) | Modulus (GPa) | Relative Cost |
|---|---|---|---|---|
| Mild steel | 7.85 | 250 | 200 | 1× |
| Stainless 304 | 8.00 | 215 | 193 | 3–4× |
| Aluminum 6061-T6 | 2.70 | 275 | 69 | 3–5× |
| Aluminum 7075-T6 | 2.81 | 505 | 72 | 5–7× |
| Copper C110 | 8.96 | 70 | 117 | 5–6× |
| Titanium Grade 5 | 4.43 | 830 | 114 | 40–70× |
| Inconel 718 | 8.19 | 1050 | 200 | 30–50× |
Last updated: June 2026 — MFGABC Manufacturing Knowledge Base