Material Properties Chart

It depends. Ti-6Al-4V (900 MPa tensile) is stronger than annealed 304 stainless (515 MPa) and 1018 carbon steel (440 MPa), but weaker than heat-treated 4140 (1,035 MPa) and 17-4 PH (1,310 MPa). However, titanium is 45% lighter than steel, giving it roughly double the strength-to-weight ratio. For weight-critical applications, titanium’s weight advantage justifies its higher machining cost.

6061-T6 offers 310 MPa tensile and 276 MPa yield with excellent corrosion resistance, weldability, and anodizing response — the versatile general-purpose choice. 7075-T6 delivers 572 MPa tensile and 505 MPa yield, nearly double the strength, but sacrifices corrosion resistance, weldability, and about 25% higher cost. Choose 6061 unless you genuinely need the extra strength.

For most indoor and general-purpose applications, 304 provides adequate corrosion resistance at a lower cost. Choose 316 when the part encounters chlorides — saltwater, de-icing salts, swimming pool environments, pharmaceutical processing — as the 2–3% molybdenum content dramatically improves pitting resistance. For better machinability, consider 303 stainless (8/10), but note it is not weldable and has slightly lower corrosion resistance than 304.

Yes, in the right application. Plastics replace metals when the part needs electrical insulation, chemical resistance, low friction, vibration damping, or significant weight reduction, and when loads and temperatures are within the plastic’s capabilities. PEEK replaces stainless steel in some medical and aerospace applications at 20% of the weight, but costs roughly 3× as much to machine as aluminum and cannot match metals’ absolute strength. Plastics creep under sustained load, soften at elevated temperatures, and expand 5–15× more than metals.

Material choice affects cost in three ways: raw material cost, machinability (cycle time and tool wear), and finishing compatibility. A part machined from Delrin might cost 15% less than the same part in 6061 aluminum because Delrin cuts faster with less tool wear. Inconel 718 costs 5–8× more to machine than 6061 aluminum because cutting speeds are roughly one-tenth and tool life is dramatically shorter. The relative cost column in the metals table provides a practical comparison.

Almost never. The strongest material that meets your minimum requirements is rarely the optimal choice because strength almost always trades off against other factors — higher-strength materials typically cost more, machine more slowly, require specialized tooling, and may introduce brittleness. A 17-4 PH stainless part (1,310 MPa) costs roughly 3–4× more to machine than a 304 stainless part (515 MPa) that would carry the same load perfectly well. Match the material to the actual requirements, not to an arbitrary safety margin.