The main objective of successful brazing and soldering is to achieve the best possible mechanical performance. The melting point temperature of each of the materials you use is one of the most important things you need to know in order to properly process your base materials, as well as your filler metal, and use the correct temperatures with your soldering iron.
What is the melting point in welding and brazing?
The melting point of a material is the temperature at which it changes from a solid to a liquid state.
You need to consider the purity of the materials you want to weld or braze. The list of melting points gives the temperatures for pure metals. When using alloys, you must take into account the different materials that make up the alloy, which often have different melting points.
It is difficult to determine the melting point of an alloy, as it is not sufficient to average the different components, especially as the proportions vary from one alloy to another.
The difference between soldering and brazing
Brazing and soldering are two different operations.
To perform a weld, you heat your base materials, as well as the filler metal in most processes, until it reaches the melting point. You must then apply the melting point temperature of the metals you are welding together.
It is therefore preferable that the various components intended for soldering have melting points close to each other.
In brazing, you do not fuse your base metals, only your filler metal. It is therefore imperative that the melting point of your filler metal is lower than that of the metals you plan to join.
You can use soft soldering or hard soldering. With the former, the melting point of the filler metal is below 450°C, with the latter, the temperature to be reached is between 600°C and 1000°C.
For soft soldering, the most commonly chosen filler metal is tin, which has the lowest melting point of the most commonly used filler metals.
When you form a solder, your filler metal must reach its melting point to transition to the liquid phase. Once placed in contact with the two parts to be assembled, it will spread and diffuse by capillary action, i.e., it insinuates itself through a network of tiny channels on the base metals.
In order for it to diffuse on both parts to be brazed, these must be perfectly prepared and cleaned. Any grease marks or roughness prevent the progression of the filler metal and weaken the brazing.
To properly prepare your surfaces once they are cleaned and degreased, you should rub them with an abrasive surface, such as emery cloth, which will create tiny scratches that promote the progression of the filler metal and ensure a stronger, more durable braze.
Melting points of the main metals used in soldering or brazing
|Raw aluminium (allumina)||1,835°C|