I've been working on a project that involves lots of hand-peening of aluminum round-headed rivets. I just ran through the first batch that were great (uncoated, soft as cheese), but when I went into the second batch I hit a snag. They're anodized, and whatever alloy the metal itself is, it's rock hard. I got all these aircraft surplus years ago and have no idea where to go now. From what I've found, the coated hard rivets are more common.
GTO(John)