The low temp melting metal appears to be similar to what I've seen in the past for "hydro" forming of copper plumbing fittings. I can't recall the name of that particular material but a search turned up this.
Field's metal, or Field's alloy is a fusible alloy that becomes liquid at approximately 62 Β°C (144 Β°F). It is named after its inventor, Simon Quellen Field.[1] It is a eutectic alloy of bismuth, indium, and tin, with the following percentages by weight: 32.5% Bi, 51% In, 16.5% Sn.
When prepared, Field's metal can be melted in hot water.
https://en.wikipedia.org/wiki/Field%27s_metal