Kurt,
I couldn't say for sure what the "Exact" compositions or hardnesses are (were) for either, but all the Stronglight literature consistently refers to their cranks as simply "Dural" (ie: Duraluminum, Duraluminium).
This was a very early aluminum alloy (pre WW-I era). The specific composition over the many years of it's use may have varied slightly. And, I suspect both brands had their own preferred proprietary formulas. The Dural also seems to have been used rather generically - just as today one might simply toss around the term "titanium alloy".
Basically, Dural had around 4% copper and also much smaller amounts of manganese and magnesium added. I've been told it is perhaps "closest" in composition to a modern 2024 aluminum alloy (CU 4.4% MG 1.5% MN 0.6%).
Kurt Sperry wrote:
Does anyone know or can perhaps even offer an informed guess which specific Al alloys were used to make Campagnolo and Stronglight (needn't limit it to those two necessarily) crankarms? I'd be interested in looking up empirical data for fatigue and physical properties.
Kurt Sperry
Bellingham WA