I can see the tool marks scratching on it sir, I think if you use a single flute bit formed into rounded edges and lower your feed rate, you'll get good results on it it usually happens when the bit itself will get gummed up by the aluminum scrappings and got rubbed the second time on the material itself.
What was your step-over set to? Using some lubricant, and making sure the swarf is constantly, cleared, with a low step over can make all the difference in the world.