The rough tin bronze also refers to phosphor bronze, as the addition of phosphorus (with a content ranging from 0.03 to 0.35) is to reduce the metal's reactivity and achieve better fluidity. Tin, with a content ranging from 1% to 10%, achieves an increase in strength by dissolving hardening and adding the tin element to the copper. The most commercially important tin bronze alloys are C510 and C521. The C510 alloy is the most commonly used tin bronze alloy, and when higher strength/forming ability components are necessary, the slightly more expensive C521 alloy is often used. The higher cost of the latter is composed of the basic cost of the added metals and the increased cost due to the influence of the added tin on hot processing. Bronze with a high tin content must be cast into strips, thus making it possible to prevent most of the cost and enabling hot crushing.
The strengthening treatment based on a higher allowable range of tin was counteracted by the low conductivity, as shown in Table 4.10. Therefore, tin-copper alloys are not suitable for high-current contacts but are better suited for signal transmission. Tin-copper has good resistance to expansion until approximately 125 degrees. The requirement for stability at higher temperatures has promoted the transformation of tin-copper alloys into condensed strengthening alloys.
The tin-copper alloy has excellent formability. For instance, since less cold treatment is required for strength, C521 offers better formability than C510. Therefore, for the same strength, the stress relaxation resistance of C521 is superior to that of C510. Typically, by increasing the number of cold treatments, the strengthening treatment of C510 slightly reduces its elongation resistance, but it can be improved by reducing the annealing degree.
Rather than saying that the stress corrosion resistance of tin-copper is affected, it is more accurate to say that the resistance of tin is enhanced. From this perspective, the difference between tin-copper and zinc-copper lies in that the increase in zinc resistance has a profound impact on the increase in stress corrosion sensitivity.