{"id":104,"date":"2022-06-05T07:19:00","date_gmt":"2022-06-05T07:19:00","guid":{"rendered":"https:\/\/mewelding.com\/?p=104"},"modified":"2024-03-18T10:48:32","modified_gmt":"2024-03-18T10:48:32","slug":"welding-magnesium","status":"publish","type":"post","link":"https:\/\/mewelding.com\/welding-magnesium\/","title":{"rendered":"Welding Magnesium – Here’s How To Do It Effectively"},"content":{"rendered":"\n
Magnesium is a very light weight metal. It has good machinability and corrosion resistance. When alloyed with small quantities of other metals such as aluminum, manganese, zinc, zirconium, etc., its\u2019 properties can be further improved to sit a variety of applications. It also has a very low melting point. However, magnesium is a very reactive metal.<\/p>\n\n\n\n
It oxidizes very rapidly when heated to its\u2019 melting point. So, a good inert gas shielding must be provided in order to prevent oxidation. Magnesium-aluminum alloys are the most commonly used. Many properties of aluminum and magnesium are similar. Some of these properties are:<\/p>\n\n\n\n
When welded with correct welding procedures, the welds made between similar base metals develop high strength that is almost equal to that of the base metals.<\/p>\n\n\n\n
The alloying elements alter the properties significantly. As the alloying content increases, the melting point and coefficient of thermal expansion decrease.<\/p>\n\n\n\n
Aluminum increases weldability when added as an alloying element, up to 10%. Adding aluminum also refines the grain structure. Zinc, when added in quantities more than 1%, increases hot shortness of the metal. This invites cracking in the joint. Hence, alloys containing high amounts of zinc are not recommended for welding due to the cracking problem.<\/p>\n\n\n\n
When thorium is added in small quantities, it improves the weldability of the metal. The cracking problem observed in zinc alloys gets eliminated. The alloys containing thorium do not require stress relief heat treatment either.<\/p>\n\n\n\n
Some magnesium alloys are prone to stress corrosion cracking. The welds that are exposed to corrosive media over a long period of time are more susceptible. The cracking occurs in the heat affected zone. For such welds, stress relieving treatment must be done, to relieve the residual stresses.<\/p>\n\n\n\n
Magnesium alloys come coated with an oil coating or a chrome pickle finish for protecting the surface during transportation and storage. Before welding, this oil film needs to be removed properly, along with oxides and any other contamination that may be present on the surface to be welded. The cleaning may be done through chemical means or mechanical means.<\/p>\n\n\n\n
Chemical cleaning yields more uniform results, hence it is the preferred method.<\/p>\n\n\n\n
It must be noted that the various cleaning solvents such as carbon tetrachloride, perchloroethylene and trichloroethylene give off toxic fumes when exposed to ultraviolet radiation of the welding arc. Hence these solvents should be removed completely before start of welding.<\/p>\n\n\n\n
The fumes that form due to the evaporation of solvents are harmful to health. One should avoid inhalation of these fumes as it can be hazardous.<\/p>\n\n\n\n
These solvents, when used without goggles, gloves, etc. cause cracking of the skin. The dry-cleaning solvent and mineral spirits paint thinner are flammable materials. Hence these solvents should be handled only in a well ventilated area, and away from open flames.<\/p>\n\n\n\n
The grease on the metal surface may be removed by using a hot alkaline cleaning compound, or a vapour degreasing system that utilizes trichloroethylene. Grease may also be removed by mechanical cleaning, by using aaluminum oxide abrasive cloth or a wire brush.<\/p>\n\n\n\n
The acids used in the cleaning of magnesium are toxic and corrosive. So abundant care should be taken to not allow such solutions to come in touch with skin, or fumes getting inhaled. Personnel protective equipment comprising of goggles, apron, gloves, etc. should be used.<\/p>\n\n\n\n
If spilled on the body, it should be washed with large quantity of water, and medical attention should be sought.<\/p>\n\n\n\n
While preparing the solution, never pour water in the acid. Instead, pour acid in the water, gradually. Mix the solution slowly. The acids give off lot of fumes that are harmful to the health. Hence handling of cleaning solutions should be done in well ventilated spaces only.<\/p>\n\n\n\n
Once the cleaning of oxides, oil, contaminating matter is completed, the part should be dipped in a solution of following composition, for three minutes:<\/p>\n\n\n\n
Chromic acid (CrO3) \u2013 24 Oz (680 gms)<\/p>\n\n\n\n
Sodium nitrate (NaNo3) \u2013 4 Oz (113 gms)<\/p>\n\n\n\n
Calcium or magnesium fluoride \u2013 1\/8 Oz (3.5 gms)<\/p>\n\n\n\n
Water \u2013 remaining quantity to make up 1 gallon (3.8 litres) of solution.<\/p>\n\n\n\n
After this, the part should be rinsed in hot water and dried with air. Similar cleaning should be done for the filler rod as well.<\/p>\n\n\n\n
Magnesium catches fire easily. Hence sufficient precautions must be taken to ensure safety of the welder and personnel working nearby. Personnel protective equipment such as goggles, gloves, etc. should be worn to protect the welder.<\/p>\n\n\n\n
The fusion temperature should be reached before solid magnesium metal ignites. Sustained burning occurs only when this temperature is maintained.<\/p>\n\n\n\n
Magnesium in powder form is a greater fire hazard. So, one should avoid having sharp filings, dust, etc. in the vicinity during welding. Magnesium in these form ignites readily if sufficient precautions are not taken.<\/p>\n\n\n\n
If a fire starts, dry sand, dry powdered soapstone, and graphite based powders acts as good extinguishing agents.<\/p>\n\n\n\n
A thorough cover of an inert gas such as helium or argon is needed for gas tungsten arc welding of magnesium. The need of shielding is accentuated by the reactive nature of magnesium. Magnesium undergoes rapid oxidation when heated to its\u2019 melting point. Proper use of inert gas prevents this oxidation.<\/p>\n\n\n\n
The welds produced with GTAW are of high quality, and of high strength. Fast travel speeds are possible. Welding can be done with direct current electrode negative polarity, or with alternating current, with a high frequency arc starter.<\/p>\n\n\n\n
For low thicknesses, both AC and DC currents are used. However, for thicknesses greater than 3\/16 inch (4.8 mm), alternating current is a better choice because of deeper penetration it provides.<\/p>\n\n\n\n
When direct current is used, helium is considered a better shielding option than argon.But, helium is a light gas. It rises up in atmosphere due to buoyancy effect. So a greater flow rate of shielding gas is necessary when helium is used. Almost three times the flow rate may be required when helium is used.<\/p>\n\n\n\n
When alternating current is used, argon is considered a better choice.<\/p>\n\n\n\n
Two commonly welded magnesium alloys are ASTM-1A (fed spec QQ-M-54) and ASTM-AZ31A (fed spec QQ-44). The former has manganese as the alloying agent, while in the latter \u2013 aluminum, manganese and zinc are the principal alloying elements.<\/p>\n\n\n\n
Base metals of thickness up to \u00bc inch (6.4 mm) may be welded with a plain square butt joint type edge preparation. It is generally enough to do welding from one side. For deeper penetration, alternating current is preferred.<\/p>\n\n\n\n
For base metals of higher thicknesses, welding should be done from both sides, if possible. This enables full penetration and lesser distortion. In such joints, the edge preparation is a double-V joint, with a small land (or root face) at the center. After welding for a few passes (or entire thickness) from one side, the weld metal is grinded off\/chipped off from the back side to remove at least one or two passes.<\/p>\n\n\n\n
This helps in removing areas of incomplete fusion, areas having oxide formation, and areas having dirt, contamination, etc. The surface is prepared to have a smooth curvature, so that weld metal can be deposited. Welding from both sides helps us to achieve a full penetration joint.<\/p>\n\n\n\n
The flow of shielding gas is started a fraction before the arc is ignited. The arc is started by scratching the surface. Or, when alternating current is used, arc may be started with a remote control switch. The arc length should be just right to obtain a quality bead. When argon is used as the shielding gas, an arc length of 1\/16 inch (1.6 mm) may be appropriate. When helium is used, an arc length of 1\/8 inch (3.2 mm) can be used.<\/p>\n\n\n\n
The following table shows the filler rod diameter and recommended welding current for various base metal thicknesses of magnesium, when welded with GTAW process. The current shown may be used with travel speeds up to 12 inches\/minute (304 mm\/minute).<\/p>\n\n\n\n
Multipass welding should be used when base metals thicker than 0.15 inch (3.81 mm) are welded. For root pass, a current of 60 amperes may be used. For subsequent passes, the currents indicated in the following table may be used.<\/p>\n\n\n\n When alternating current is used to TIG weld magnesium, the filler rod should be held as parallel to the ground as possible. The torch should be held almost perpendicular to the ground, with a slight travel angle. The right torch and filler metal position is illustrated in the figure below.<\/p>\n\n\n\nMetal thickness<\/strong> (inch)<\/strong><\/td> Diameter of filler rod<\/strong> (inch)<\/strong><\/td> Welding current<\/strong> (amperes)<\/strong><\/td><\/tr> 0.030<\/td> 1\/16<\/td> 20<\/td><\/tr> 0.040<\/td> 1\/16<\/td> 30<\/td><\/tr> 0.050<\/td> 3\/32<\/td> 35<\/td><\/tr> 0.060<\/td> 3\/32<\/td> 45<\/td><\/tr> 0.070<\/td> 1\/8<\/td> 55<\/td><\/tr> 0.080<\/td> 1\/8<\/td> 60<\/td><\/tr> 0.090<\/td> 1\/8<\/td> 65<\/td><\/tr> 0.100<\/td> 1\/8<\/td> 70<\/td><\/tr> 0.125<\/td> 1\/8<\/td> 75<\/td><\/tr> 0.150<\/td> 5\/32<\/td> 80<\/td><\/tr> 0.200<\/td> 5\/32<\/td> 90<\/td><\/tr> 0.250<\/td> 5\/32<\/td> 100<\/td><\/tr> 0.500<\/td> 5\/32<\/td> 115<\/td><\/tr> 1.00<\/td> 5\/32<\/td> 130<\/td><\/tr><\/tbody><\/table><\/figure>\n\n\n\n Welding Technique<\/h3>\n\n\n\n