What is the box made out of? Steel? Aluminum? Worried about corrosion streaks.

Thank you for your question. Sigma's Weatherproof round electrical box is made out of Aluminum. This product is constructed with die-cast metal that prevents moisture penetration in outdoor applications. If you have any additional questions regarding this product, please feel free to reach out to our customer support team directly at: www.sigmaengineeredsolutions.com/company/contact-us/