aluminum PCB soldering techniques for prototypes
The solder reflow heat mass is significantly greater.  You may need some forced air for ramp-down and a thermocouple probe to "profile" a bare board to match the LED recommended ramp rates , peak liquidus dwell and cooling rates to prevent solder stress failures.

Assembly line process engineers do this with a thermally protected data collection module and slow down the conveyor speeds to absorb the higher heat mass and accelerate the temperature rise in the number of zones in their control, yet too slow is a reliability issue for LEDs and the overall time to ramp up and down must not be exceeded for this reason.

So do a dry run and get a digital timer.

If you do not have thermocouples , estimate the liquidus point when a tiny blob of solder melts and the duration it is melted. and your overall profile time from the datasheet. Avoid too slow and too fast as the wire bond may shear inside.

The main difference with FR4 is the massive heat sink effects of Alum. compared to FR4 requires a lot of power based on the 'C/W rating of the board. You can do the math for Watts and T rise.

Ideal process time 5 minutes, max 6 minutes

details

http://www.cree.com/~/media/Files/Cree/LED%20Components%20and%20Modules/XLamp/XLamp%20Application%20Notes/XLampXBD_SH.pdf