Aluminium bronze between 5% to 11% aluminium by weight, the remaining mass being copper. This alloy has some incredible properties when compared to other alloys. Its tougher and harder than both tin-bronze and iron, although not as hard as steel. http://en.wikipedia.org/wiki/Aluminium_bronze
Its more corrosion resistant than tin-bronze which is impressive because there are pieces of usable tin-bronze that are many thousands of years old.
It can disinfect itself through the oligodynamic effect.http://en.wikipedia.org/wiki/Oligodynamic_effect
It can be lost wax casted into almost any shape. For sharp tools you can cold work (Wack it with a hammer when cold) the edges to make them harder before grinding them into shape.
Most importantly this alloy is made from two of the most common and most corrosion resistant metals that will be left over after the collapse of civ.
Here’s a good site that has information on how to cast aluminium ingots from pop cans http://www.backyardmetalcasting.com/index.html
This site has lots of information on bronze age casting methods http://www.umha-aois.com/index.html
I think that while scavenging tools will work well during the transition stage, if we want our feral cultures to have good metal tools after the rusting stage I see only bog iron or copper alloys.
To make tools from bog iron you need alot of skill, charcoal, time and equipmenthttp://www.hurstwic.org/history/articles/manufacturing/text/bog_iron.htm. Which is ok for sedenary farmers like the vikings or maybe forest gardeners but for semi-normadic hunter-gardeners or fully normadic hunter-gathers its going to be more difficult to do because tools from bog iron requires time staying in one place and highly specialised division of labor.
Casting copper alloys requires less skill, charcoal, time and equipment and are therefore more suitable for manufacture in normadic tribes. Of copper alloys Aluminium bronze is set to be the most useful.
I’m going on a two day course learning bronze age casting techniques with tin-bronze then I’m going to attempt to cast a tool out of Aluminium bronze. So I’ll let you know how I get on.
With tin bronze the addition of more Tin increases the hardness of the alloy, but also causes it to become more brittle. Therefore a balance of these qualities has to be found according to the use of the finished object. For example, an axehead consists of about 90% Cu to 10% Sn whereas a razor blade consists of about 80% Cu to 20% Sn. I need to experiment to find out if the same is true for Aluminium bronze.
Hope this is helpful