Two aluminum alloys. Different strengths. Different uses.

7075 billet is typically 20–40% more expensive than 6061 per kg. The total finished part cost difference is usually less than the raw material ratio because machining is similar. For a typical CNC part, 7075 finished parts cost 10–25% more than equivalent 6061 parts. If the strength premium is used (thinner walls, less material), total weight and cost can actually decrease with 7075 despite higher unit material cost.

7075 contains zinc (5–6%) as a primary alloying element. During welding, the heat-affected zone (HAZ) experiences solution-loss of the strengthening precipitates, dropping strength by 50–70%. The weld itself is susceptible to cracking. While 7075 CAN technically be welded, the strength loss defeats the purpose of using 7075. If welding is required, 6061 is the right choice. For joining 7075 parts, use mechanical fasteners or friction stir welding (specialty process).

6061 anodizes more consistently. 7075's zinc content causes slight variability in dye absorption, sometimes resulting in blotchy appearance or color variation. For premium cosmetic anodized parts (consumer electronics), 6061 is preferred despite lower strength. For 7075 cosmetic work, specific dye chemistries and bead-blasting before anodize improve uniformity.

T6: standard temper, solution treated and artificially aged. T651: T6 with stress-relief by controlled stretching (1–3%). T651 has reduced internal stress, better dimensional stability during machining (less warping after material removal). For large or thin parts where warping matters, T651 is worth the slight cost premium. For small parts with thick cross-sections, T6 is fine.

Occasionally. 2024-T3: slightly higher fatigue strength than 7075, used in fatigue-critical aerospace (wing skins). 2014-T6: similar strength to 7075 with better weldability. Both are less common than 7075 but appropriate for specific applications. For most "aerospace structural aluminum" needs, 7075-T6 is the default — availability, established processes, and familiarity drive this.

Medium-complexity machined bracket 80 × 60 × 15 mm, 1000 pcs: 6061-T6 bracket ~$12–18 per part. 7075-T6 equivalent ~$15–22 per part. Surface finish and anodize similar cost. For high-volume production where 6061 strength is adequate, 6061 saves $3000–4000 per 1000 parts. When 7075 strength is actually needed (aerospace, defense), the premium is usually justified.