Brass wall art can hold up well outdoors but darken and develops a unique patina over time. Patina is not corrosion or rust but a film resulting from oxidization that adds to the character of the art piece. You can polish the brass to keep it shiny for a more extended period.
Keep in mind that some brass wall art has non-brass components that may rust over time. Also, the wall attachments might not be designed to withstand wind or other sources of damage.
Check the individual art piece’s instructions for specifics on whether it is designed for outdoor use. In some cases, outdoor use may void the warranty.