Yes, it can do macro but not 1:1. For macro function, 28-75 is better, since it has a longer range. It can do 1:3.9 (at 75mm) compared to 1:4.5 (at f=50mm MFD 0.27m) on 17-50.
Below is the specs that I got from Tamron site, just for comparison:
[AF28-75mm F/2.8 XR Di LD Aspherical (IF)]...