Non-ferrous alloys — composition identification: Which composition most closely represents a typical silicon bronze used for corrosion-resistant hardware and marine fasteners?

Introduction / Context:
Silicon bronze is a family of copper-based alloys valued for their corrosion resistance, strength, and excellent castability/weldability. Designers and fabrication engineers frequently need to distinguish silicon bronze from brasses (Cu–Zn) and tin bronzes (Cu–Sn) when selecting fasteners, pump components, and marine fittings.

Given Data / Assumptions:

• The term “silicon bronze” refers to common wrought/cast grades where copper is the major element and silicon is the main alloying addition.
• Minor manganese is often added to improve strength and deoxidation.
• We seek a representative textbook composition, not a proprietary variant.

Concept / Approach:
Typical silicon bronze grades contain very high copper, with silicon in the low single digits. A canonical composition cited in handbooks is approximately 96% Cu, 3% Si, and 1% Mn. Silicon strengthens the copper matrix and improves fluidity during casting while maintaining good corrosion resistance. By contrast, compositions rich in zinc are brasses, and those rich in tin are tin bronzes (phosphor bronze when P is present). Extremely high silicon (for example 20%) is unrealistic for silicon bronze and would not exhibit the expected properties or phase balance.

Step-by-Step Solution:
Recognise that silicon bronze must be Cu-rich with small Si additions.Scan options: only one choice keeps Cu near mid-90% and Si near 3% with about 1% Mn.Reject alternatives that are brasses (Cu–Zn dominant) or tin bronzes (Cu–Sn dominant).Select 96% Cu, 3% Si, 1% Mn as the correct composition.

Verification / Alternative check:
Standards for silicon bronze fastening and welding filler (e.g., common C65500-type compositions) cluster around a few percent silicon with the balance copper and minor Mn.

Why Other Options Are Wrong:
60% Cu, 35% Zn, 5% Mn describes a high-zinc brass, not silicon bronze.

88% Cu, 10% Sn, 2% Zn is a tin bronze (phosphor bronze family), not a silicon bronze.

76% Cu, 20% Si, 4% Zn has unrealistically high silicon for service bronzes.

70% Cu, 28% Zn, 2% Al is again a brass variant.

Common Pitfalls:
Confusing brasses and bronzes solely by colour; relying on trade names instead of composition ranges.

Final Answer:
96% copper, 3% silicon and 1% manganese