Whatever's on special that says "non-caustic", will suit alloy parts. Active ingredient is usually ethanolamine. It also cleans laminate benchtops like new, so you can tell the better half you want to help with the housework; that's why to buy it in bulk...
Two applications are needed on seriously dirty stuff, with a good scrub inbetween,
before rinsing. Apply only to dry surfaces; water reduces effect immensely.
Caustic sprays will do fine on cast iron, but so will a laundry tub of hot water and 1kg caustic soda.
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Soak minimum of 2 hours, scrub and soak again. The leftover grungy water gets dug into my excess dirt pile (currently about 8m³).
Backgrounds for photography are a hassle. White often gives averaging type light meters a false reading and the object will be too dark. Light grey-white concrete seems to do nicely. I often rub a yellow crayon across the tops of cast part numbers, to show more clearly.
Clean stuff can be phosphated if iron or steel, and wrapped in plastic masking. The "Kephos" product sandblasters use will work well instead of phosphoric solutions. For that matter, I pay about $20 to get a degreased, stripped down iron head garnet blasted inside and out, and phosphated. Means that whenever you want to measure something or just handle it, there's no mess.