Drill bit question

The tips are cobalt and tungsten carbide. Any idea why hardened steel, brick, porcelain, wood are fine to drill with these but mild material like copper, aluminum, angle iron and galvanized are not?

Here's the link:
Link

Thanks James

Could be like Davis said--the bit's clearance angle may not be enough to allow the shavings to curl away. Whatever the reason though I wouldn't spend any extra money on special bits for drilling mild steel. I've used the standard HSS bits for many years with good success and have even drilled stainless steels up to 3/4". The key is to keep your bits sharp, use slow spindle speeds and use lubricant/coolant or thread cutting fluid. For light work, Gunk engine cleaner makes a good lubricant/coolant or for heavy work I like a product called "TAP Magic". They changed the formula a few years back and it's not as good as it used to be but for drilling and tapping, its good stuff. If you're in the field, even water works better than running a bit dry and hot.