A method of forming a tube for a heat exchanger includes advancing an expansion tool into a tube a first time and engaging the expansion tool with the tube to expand the tube diametrically at least partially along a length of the tube. The expansion tool is at least partially retracted from the tube. The expansion tool is advanced into the tube one or more subsequent times thereby engaging the expansion tool with the tube one or more subsequent times to further expand the tube at least partially along the length of the tube.