Patent ID: 8640766

Claim:
A heat exchanger tube precursor comprising an Al alloy extruded tube, and a flux layer including a Si powder, a Zn-containing flux, and a binder formed on an outer surface of the Al alloy extruded tube, wherein an amount of the Si powder applied on the Al alloy extruded tube is in a range of 1 g/m 2 or more and 5 g/m 2 or less, an amount of the Zn containing flux applied on the Al alloy extruded tube is in a range of 3 g/m 2 or more and 20 g/m 2 or less, and the Si powder has a particle diameter distribution such that 99% particle diameter (D 99 ) is 5 μm or more and 20 μm or less, and an amount of coarse particles having diameters of not smaller than 5 times (D 99 ) is less than 1 ppm by volume, where (D 99 ) denotes a critical diameter defined such that cumulative volume of particles not larger than (D 99 ) constitute 99% by volume of all the particles, wherein 50% particle diameter (D 50 ) of the Si powder is (D 99 )×0.05 or more and (D 99 )×0.7 or less, where (D 50 ) denotes a critical diameter defined such that cumulative volume of particles not larger than (D 50 ) constitute 50% by volume of all the particles.