On Fri, 29 Jun 2012 05:48:18 -0700, George Herold wrote:

(reposted from SED)
I want to try soldering some aluminum plate (0.032€�) onto each side of a
brass cylinder. When trying to solder aluminum in the past I failed.

Famously, Al quickly acquires a tough oxide layer of Al2O3 in air, and
nothing solders to that. There are ultrasonic iron tips that break up the
oxide so quickly and thoroughly that it can't reform before the solder
gets to it, but they are too rare and pricey.

I actually had success with the method I heard about here long time ago:
cover up your soldered area with light oil (engine/turbine) and scratch
the aluminum surface vigorously under the oil with steel brush or a
scraper, then apply hot iron loaded with solder. I used regular SnPb.