dull bit or really hard aluminum?

Almost looks like there is a sleeve in the hole in the photo... Incorrect speed, dull bits or incorrect bit angle will cause excessive friction and heat. Aluminum is "gummy" when cutting and drilling and chip evacuation is important. A sharp bit and peck drilling and lifting the bit out completely each peck while using a coolant or cutting oil will keep the bit cool and avoid the issues it looks like you're having.
 
Dull bit, but one other consideration- is that 6061 heat treated (T6)? Depending on the needs of its original source, it may or may not be.

Also, I am not a fan of 3-in-1. Alumicut or any other engineered cutting fluid would be preferable to a general purpose household oil. A squeaky cabinet hinge does not have the same heat and stability requirements as a cutting tool.
 
Many speed charts are intended for maximum material removal in the least amount of time, for production shop needs. Not as important for home/hobby situations. 1000 rpm or so would be fine for 1/4" drill in aluminum, with a sharp bit.
M
 
We always twist the bit by hand against a finger tip to feel if it is sharp.

Aluminum can be nasty stuff

Extruded aluminum is real gummy and will make a wad over the cutting edge and give similar results.

A drop of oil in the hole helps as well as tuning up cutting edges.

Sent from my SAMSUNG-SM-G930A using Tapatalk
 
I say it s a bushing. Heat expanded the hole and drill pressure pushed the bushing down.
 
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