Six pack Abs for a skinny guy

[onh1986]

Hi,
I'm mild skinny guy 140 lbs and %9 total body fat, when I had started working out, I was almost 120 lbs, now my arms and back are getting little bigger after 4-month-exercise.
But I'm still confused in Ads exercise, I do Abdominal Crunch 3 sets of 10 reps every other day, I know it's not that much, but I not sure whether if it is enough to get six pack abs or not, I increase the Abdominal Crunch weight 5 lbs every two week, I'm now at 90 lbs.
If I keep that way, how long does it take to notice the six pack?
Any further suggestion would be appreciated.

Thanks

[SUANHEI]

Hello everybody. I did deadlift about a year ago with heavy weight (for my weight) and I did it with badly curved back