Dacia Sandero Stepway Wiper Arm

[hairygrape]

One of the front wiper arms on the wife's car has a snow-white area around the arm hinge that I'm totally baffled about. The arm itself is matt black but it looks as if the paint has flaked off on an area around the size of a 2p coin near and partially over the hinge at the bottom. The white area is rough to the touch and looks sort of granular in appearance. I've not tried to scrape the area as I'm afraid of causing damage. There's no sign of rust around the area either.
I've got no idea what metal or alloy the arm is made off and I'm at a loss to know what to do. The integrity of the arm seems unaffected and the area is on the front surface of the arm with some creep towards the hinge itself. Rust removers/converters seems inappropriate as it doesn't look like rust. It's certainly not bird poo either, which was my first thought when I saw it!
How do i treat the area? Is it possible to buy some sort of paint to blacken the area ? I've no idea what sort of paint I need given that the arm is matt black. Is there such a thing as black wiper arm paint?
I'd be grateful for any help over this. Thank you.

[mjwman]

Seems like alloy corrosion. Take it off rub it down thoroughly then spray prime and use a matt or satin paint like Hammerite and all should be well.
Or buy a new arm....

[hairygrape]

Thank you mjwman. Would you advise that I use Hammerite spray paint as well or could I paint it with a brush. Thank you again.