A PBS show on a few nights ago had a history of aluminum and its uses. In the show it mentioned aluminum is too soft when pure so copper was added but the discoverer found even after copper was added it was still too soft, he got fed up went away for a few days and when he came back the alloy was harder; age hardening.

My phone was damaged and I wondered if my keys scratched my SG3 smartphone, Gorilla Glass has a hardness from what I have read anywhere from a 3 to a 6 but corundum (oxidized aluminum) has a Mohs hardness of 9. Then I found out scratch resistance is not hardness. I think the SG3 screen's scratch resistance is significantly inferior to the SG2 screen.