I don't know about the 'when' , but I do know that cadmium plating is a very good corrosion deterrent .
Not to muck up your thread , but here's an FYI ( from Wiki ) :
Cadmium plating
Cadmium plating is under scrutiny because of the environmental toxicity of the cadmium metal. However, cadmium plating is still widely used in some applications such as aerospace fasteners and it remains in military and aviation specs however it is being phased out due to its toxicity and corrosive properties.[4]
Cadmium plating (or "cad plating") offers a long list of technical advantages such as excellent corrosion resistance even at relatively low thickness and in salt atmospheres, softness and malleability, freedom from sticky and/or bulky corrosion products, galvanic compatibility with aluminum, freedom from stick-slip thus allowing reliable torquing of plated threads, can be dyed to many colors and clear, has good lubricity and solderability, and works well either as a final finish or as a paint base.[3][5]
If environmental concerns matter, in most aspects cadmium plating can be directly replaced with gold plating as it shares most of the material properties, but gold is more expensive and cannot serve as a paint base.
