I remember reading that Austrians used pig iron for their cuirass, for their cuirassier troop. Whereas the same troop were issued helmets made from bronze with steel caging. Other people said that was false and their cuirass was made from steel with an iron cylinder pressed in the edges, and their helmets were predomintately steel.
I am assuming that a lot of it was just depending on the regiment/armourer/country? And that bronze/brass/iron/steel were all used... I also remember reading how a lot of British swords had bronze in their hilts.
Your post seems to lack a direct question. Regardless, I shall attempt to answer.
Weapons and Equipment of the Napoleonic Wars - Philip J Haythorthwaite
...in France the first general issue was made in 1802, though the 7th Cavalry (ex-Cuirassiers du Roi of the Ancien Regime) had worn them before. The French pattern consisted of a heavy iron breastplate and a lighter backplate, joined together by shoulder straps and secured by a waist-belt buckled at the front and bolted to the backplate. The shoulder-straps constituted an extra protection, being made of overlapped brass scales or occasionally chain or leather. Two later patterns of cuirass ('Mk II' after 1806 and 'Mk III' in 1809) differed only marginally, though officers' cuirasses were more decorative, with gilded rivets and ornamental straps. From 1810 French carabiniers wore similar cuirasses, covered with thin brass sheeting (copper plated for officers). Protecting the jacket from wear the cuirass lining or 'cuffs' was scarlet for cuirassiers and light blue for carabiniers , of cloth with white lace edging for troopers and silver lace for officers. The usual German cuirass consisted of a front plate alone, with cross-straps on the wearer's back, often the front enamelled black (as worn by Austria and Russia).
on helmets
Cavalry helmets cannot really be considered 'armour': even the French iron cuirassier helmets and the German boiled-leather types would not stop a hefty sword cut.
Not really an ideal answer I know but without a direct question it's very hard to answer.