Many foundries at a percent or two of lead to their brass or bronze castings to make them sound.
California, where for some reason they don't like to drink lead, prohibits this for plumbing fixtures.
Ho hum.
Except if you heat such brass nice & hot to bend it that lead, which exists as small particles, melts. The molten lead runs between the crystal boundaries & your brass guard behaves like lead.
It likely cracks or crumbles.
Best to bend cold, or anneal, cool then bend.
Your P.I.T.A. Metallurgist