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Welding-aluminumand Aluminum AlloysSOLUTIONS with Effective, Powerful AdviceWelding-aluminum, aluminum welding, joining of aluminum alloys, spot and seam welding aluminum alloys, brazing aluminum, cast aluminum welding, repairing aluminum by welding, aluminum fabrication, aluminum weldability, unweldable aluminum alloys, easy-to-weld and hard-to-weld aluminum alloys, material identification, heat treatments, microstructures, welding information, welding links, welding tips, improving welding results, joining questions needing answers: these are some of the items developed in this Site for the benefit of interested readers.
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What is in here for me? Welding-aluminum is not difficult, provided you refer to a weldable kind of it, once the problems are clarified. You certainly know all you need on the materials you usually work with. What about other materials? Is there anything worth knowing for welding them? What material conditions affects weldability? This Site is designed to cast light on the kind of problems you may meet when confronting a new Welding-aluminum job, to help you, in case you wonder, to know in advance what to do. When needed, write your problem down and send it over to us. For any questions on these subjects write us by e-mail. Click on the Contact Us Button in the NavBar. Welding-aluminum is concerned with aluminum alloys weldability. This is a qualitative assessment of the material suitability to be welded by a certain process in a properly designed structure under given conditions, to present a specified quality level (that is without unacceptable defects), and to perform in service according to given requirements. Therefore... ...materials like aluminum alloys may show different weldability in different conditions for different processes but may still be satisfactorily welded with particular precautions, generally spelled out in detailed procedures. Welding-aluminum is easy for certain aluminum alloys, in that it can be done without special precautions by most welding processes under most conditions to provide acceptable and consistent welds. It should be remembered however, that aluminum produces easily, just by sitting in air, an impervious layer of aluminum oxide which protects the surface from corrosive attacks, but also interferes with welding. Special cleaning procedures are required to remove the oxide before welding or brazing. Tip!: If you are in the design stage, it is strongly recommended that, beside other things, you consider also, or ask about, the weldability of the material you help to select. But if you are past that stage and you have to weld whatever material other people selected, well then the best thing you can do is to be sure it is weldable, to know what material it is and what is its weldability, to look for an appropriate process and a suitable procedure. Don't skip this one... As the question of Material identification for Welding-aluminum is going to play an important part in the quest for the best welding procedure we reserve this issue for a dedicated page that you can read by clicking on the underlined title. Note: For informations on welding characteristics of other Materials see the related pages listed as links in a further section of this page.
Welding-aluminum alloys raw materials is performed on Castings, Forgings or Wrought product forms. The properties which make these materials useful for various applications are mostly low density (specific weight), which is about one third that of steel, ease of fabrication, good thermal and electrical conductivity, pleasant appearance, corrosion resistance and also useful relative strength. Welding-aluminum can be performed on alloys of different properties. The outstanding characteristic of aluminum is its lightness, which is put to profit in transportation, cars, boats, trains, aviation, and moving machine elements. Some of the alloys can be hardened by special procedures of heat treatment, while others can only be strengthened by cold work and deformation. After Welding-aluminum, it can be made impervious to atmospheric corrosion, a property which contributes to its selection for decorative and structural elements of architectural construction. Aluminum is easily cast, forged, formed, welded (within certain limits) and finished to pleasant appearance. Different protective coatings, like anodizing, some with special hardness, can be built integrally upon the external surfaces. Although less than copper, aluminum is a good conductor of heat and electricity. Aluminum scrap is valued because recycling is less energy intensive than primary production. Aluminum alloys wrought products are listed usually according to the Aluminum Association designations, making use of a number where the first figure represents a class and the other three represent a specific type. The temper convention defines the condition of different products: O is annealed condition. T- followed by a number indicates solution and aged condition. H- followed by a number indicates the degree of strain hardening of non heat treatable alloys. F is as fabricated. What is the difference?... Welding-aluminum of non heat treatable alloys (of the 1xxx, 3xxx, 5xxx, classes) is readily performed by most processes except that if their elevated mechanical properties were obtained by mechanical work (also called strain hardening), the strength can be locally reduced by the weld heat and cannot be restored. Heat treatable aluminum alloys (of the 2xxx or 7xxx classes) include finely tuned proportions of certain elements (i.e. copper, zinc etc.) that through a delicate play of solutioning (by heating and rapid quenching) and precipitation out of solution in well defined procedures (either by natural aging or by heating), produce improved mechanical properties as explained in the following. Welding-aluminum on these alloys in heat treated conditions is less favorably performed and only with special precautions or by certain processes only (Resistance welding), as briefly detailed in the following.
To put some order in the above we should first understand the structure of hardenable Aluminum Alloys. In very simple terms, Aluminum Alloys of Type 2xxx include about 5% of copper which confers special properties to the material. It all depends on a property called solubility, that is the capacity of an element of being dissolved into another in what is called solid solution. The favorable situation arises when at room temperature the solubility is limited, while it is larger at a more elevated temperature (less than the melting point). When this situation arises, at the higher temperature the atoms of the less abundant element take definite positions in crystals, which are the building blocks of the alloy, but at room temperature, say after cooling from melting, they group in disorganized lumps. With some elements, like copper in aluminum, a strange effect appears. While heating at a certain temperature, below the melting point, all of the copper present enters into uniform solution, like sugar in water (except that we are talking here of Solid Solution). A property called diffusion provides the driving force for displacing copper atoms into the matrix (the mass) of aluminum, so that the density of copper atoms, given sufficient time, is homogeneous or equal in each and every point. When the material is cooled back to room temperature one of two different things may happen. If cooling is slow, copper atoms driven by the reduced solubility at lower temperature, will again group themselves in lumps, useless for providing improved properties. But if cooling takes place immediately, by quenching the material into water, the copper atoms have no time to diffuse back, so they remain in a so called supersaturated solution at room temperature, which is a not so stable condition. Then just by themselves, in about four days, they precipitate out of solution in tiny particles or "phases", in a microstructure which exhibits much higher mechanical properties (strength and hardness). This process is called natural aging. A similar process called artificial aging, is produced much more quickly by heating at about 120 to 180 0C (250 to 360 0F). That is why the complete process is called solutioning and precipitation hardening. Welding-aluminum of these types, will not only hurt the mechanical properties, but also the corrosion resistance, practically destroying the properties that made them useful: therefore they are considered non-weldable, except by resistance welding. Tip!: If an unscrupulous subcontractor attempts to repair weld an unweldable aluminum alloy, against the rules, his mischief will most likely be detected visually after anodizing... Other heat treatable alloys (of 6xxx class) are weldable but the properties should be restored after welding, if required, by renewed heat treatment. Cast Aluminum Alloys can also be classified according to their specific weldability. Welding-aluminum alloy castings for repair can be done in certain cases only before hardening by heat treatment. Dip Brazing of aluminum alloys is briefly reviewed in a related page on Brazing Heating. See also our NEW Page on Brazing Aluminum. An article on brazing Aluminum to Steel explaining how two companies providing solutions to the automotive industry developed two different solutions to the problem of joining (by fusion) incompatible materials, was published in Issue No. 43 of Practical Welding Letter for March 2007 (section 4). Click on PWL#043 to read it. An Article on Low Porosity Laser Welding was published (11) in
AA ADM-1 ANSI/AWS D1.2/D1.2M:2003 NEW RESOURCES
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We discuss some of the processes applicable to Welding-aluminum and its alloys in another page, readily accessible by clicking on the underlined title, as indicated hereafter: Aluminum welding processes. Metal Matrix Composites An Article on Metal Matrix Composites was published (11) in Issue No. 47 of Practical Welding Letter for July 2007. Click on PWL#047 to read it.
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Let us remind you that you are entitled, if you are interested, to a FREE subscription to our Practical Welding Letter, that we will send to you periodically for as long as you want. To reach a Page, listing the most important Articles from Past Issues of Practical Welding Letter, click on Welding Topics. And also to a FREE download, right to your computer, of our book in pdf format, designed to stress important points on PRACTICAL HARDNESS TESTING MADE SIMPLE. Click here Even if you know what Hardness Testing is all about, you might discover a few useful ideas, with direct application to your welding projects.
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