Low temperature aluminum brazing

Bonnewagon

Geezer
Sep 18, 2009
8,539
113
Queens, NY
I'm sure you have all seen the YouTube videos showing the process of using a low melting temperature aluminum rod to braze aluminum with a propane torch.
The concept is that aluminum melts at around 1200° or so and the rods melt at 600-700° so the parent metal is not destroyed. I had a situation where the cavitation plate on an outboard motor gearcase cracked and broke off. That seemed like a natural for this process. I purchased the special low temp rods and gave it a shot. After grinding the parts clean I spent a LOT of time heating them with the propane torch. The broken-off part got hot enough for the rods to melt and flow just like in the videos. But the gearcase itself was so big it acted as a huge heat-sink and never could reach the temperature so the rods would melt. My conclusion is that on small or thin items this process is a winner. But on anything really large the heat dissipates so fast the process is useless. As for strength, the broken part had a lot of the melted rod so securely attached that is was a huge chore to grind it all off so I could get the part TIG welded. It really is stronger than the part you are fixing. You might be tempted to use an acetylene torch to get that big part hot enough. But acetylene runs at about 5000° and you risk ruining the part. If I get to fix something smaller I will update the results.
 
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