what is a 1974 the aluminum penny was adopted?

France tried aluminium coins post war but they gave up as they did not have the heft of heavier metals so were perceived as cheap and nasty.
 
Japan has used aluminum for ¥1 coins since the mid-50s, no problem. They're kind of cool in that because mass (1 gram), they are sometimes used as weights for home scale calibration. Also, cooler but less useful, because the distribution of that mass, if placed with a little care, they won't break the sufrace tension of water, and thus will float.
 
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