What would be the application for these sheet metal brackets and do you have any load-bearing requirements they need to meet?

Aluminum is a lightweight material and has good corrosion resistance. But I’m afraid it may no be the best choice for your heavy-duty applications. Steel would be much better if strength and load-bearing are an essential requirements. But you can also find high-strength aluminium alloys that can carry significant weight. These alloys can also withstand outdoor weather conditions. I would say it mostly depends on your application and specific needs. Hope this helps!

Generally, high-strength aluminum alloys are more expensive than common steel grades. Plus, if the brackets support conveyor components (inside a machine I guess), they don’t need to have properties for outdoor use, such as corrosion resistance. So steel seems to me a better option in terms of cost-efficiency.