Four questions.
The right alloy.
Every time.

Match to the dominant requirement. Choose metal when: high structural loads (> 100 MPa), high temperature (> 150 °C continuous), strict dimensional stability under humidity and load, electrical conductivity needed, or wear resistance critical. Choose plastic when: weight matters, corrosive environment, electrical insulation, noise dampening, lower cost per complex geometry, or safety from injury (smooth soft surfaces).

Aluminum 6061-T6 for 80% of general-purpose metal parts. Good strength (276 MPa yield), excellent machinability, corrosion resistant, anodizes beautifully, weldable, available everywhere at reasonable cost. Only move away from 6061 when you have a specific reason: need higher strength (7075), higher corrosion resistance (316L, titanium), or higher temperature (titanium, Inconel).

ABS for cost-sensitive cosmetic applications, nylon (PA66) for mechanical parts. ABS is cheap, impact resistant, paintable, platable, and handles any cosmetic enclosure. Nylon is tough, wear-resistant, and handles moderate loads. Upgrade to polycarbonate for higher impact or transparency, Delrin for precision mechanical, PEEK for extreme temperature or biocompatibility.

Material cost per kg is only part of the picture — manufacturing cost depends on machinability too. Approximate relative raw costs: commodity steels ($2–4/kg), aluminum 6061 ($6–10/kg), stainless 304 ($8–15/kg), brass ($10–15/kg), titanium Gr.5 ($50–80/kg), PEEK ($300–500/kg). Machining cost scales with hardness and cutting speed, so a $5 steel part and $50 titanium part can easily become $50 and $400 finished.

Yes — our engineering team has 14+ years of material selection experience across aerospace, medical, automotive, robotics, consumer electronics and semiconductor applications. Free material consultation included with every quote request. If you're unsure between two materials, describe the functional requirements and we'll recommend with reasoning.