Aluminum Welding Tips and Tricks


BY FRANK ARMAO, SENIOR APPLICATION ENGINEER, THE LINCOLN ELECTRIC COMPANY

Aluminum is being specified at present in increasingly more functions due to its many benefits. Aluminum is light-weight (approximately1/Three the burden of metal), has glorious electrical conductivity and higher corrosion-resistance properties than metal. As its development accelerates, operators who’re used to welding on metal might want to study the “ins and outs” of welding aluminum.

Listed here are among the most ceaselessly requested questions concerning the welding of aluminum, and their solutions from an knowledgeable:

1. How do I weld 7075?

You may’t, no less than not for structural work. Most aluminum alloys are weldable, however there are a good variety of them that aren’t, together with 7075 aluminum. The rationale 7075 is singled out on this instance is that it is without doubt one of the highest energy aluminum alloys. When designers and welders search for an aluminum alloy to make use of, many will begin by reviewing a desk that lists all the aluminum alloys and their strengths. However what these newcomers don’t understand is that few of the upper energy aluminum alloys are weldable – particularly these within the 7000 and 2000 sequence – they usually shouldn’t be used.

The one exception to the rule of by no means utilizing 7075 for welding is within the injection molding trade. This trade will restore dies by welding 7075 – nevertheless it ought to by no means be used for structural work.

Listed here are some easy pointers to comply with when selecting aluminum alloys:

  Primary Alloying Components
1000 sequence Pure aluminum
2000 sequence Aluminum and copper. (Excessive energy aluminum used within the aerospace trade )
3000 sequence Aluminum and manganese. (Low- to medium-strength alloys, examples of merchandise utilizing these alloys are beverage cans and refrigeration tubing)
4000 sequence Aluminum and silicon. (Most alloys on this sequence are both welding or brazing filler supplies)
5000 sequence Aluminum and magnesium. (These alloys are used primarily for structural functions in sheet or plate metals — all 5000 sequence alloys are weldable )
6000 sequence Aluminum, magnesium and silicon. (These alloys are heat-treatable and generally used for extrusions, sheet and plate — all are weldable, however could be crack-sensitive. By no means attempt to weld these alloys with out utilizing filler steel)
7000 sequence Aluminum and zinc. (These are excessive energy aerospace alloys which will produce other alloying parts added)

Lincoln means that you probably have a have to design one thing of high-strength aluminum, look to a 5000 sequence excessive magnesium alloy as an alternative of a 2000 or 7000 sequence. The 5000 sequence alloys are weldable and can produce the perfect outcomes.

2. Why is my aluminum weld a lot weaker than the mother or father materials?

In steels, a weld could be made as sturdy because the mother or father materials, however this isn’t the case with aluminum. In nearly all cases, the weld shall be weaker than the mother or father materials. To additional perceive why this happens, let’s take a look at the 2 classifications of aluminum alloys: heat-treatable and non-heat-treatable. The latter class is hardened solely by chilly working which causes bodily adjustments within the steel. The extra the alloy is cold-worked the stronger it will get. However, while you weld an alloy that has been cold-worked, you regionally anneal the fabric across the weld in order that it goes again to its zero tempered (or annealed) situation and it turns into “gentle”. Due to this fact, the one time within the non-heat treatable alloys which you could make a weld as sturdy because the mother or father materials is while you begin with zero tempered materials.

With heat-treatable aluminum alloys, the final warmth therapy step heats the steel to roughly 400° F. However when welding, the fabric across the weld turns into a lot hotter than 400° F so the fabric tends to lose a few of its mechanical properties. Due to this fact, if the operator doesn’t carry out post-weld warmth therapies after welding, the realm across the weld will change into considerably weaker than the remainder of the aluminum — by as a lot as 30 to 40 p.c. If the operator does carry out post-weld warmth therapies, the proprieties of a heat-treatable aluminum alloy could be improved.

The next is a information as to which sequence of aluminum alloys are heat-treatable and which aren’t:

Warmth-treatable sequence: 2000, 6000, 7000.

Non-heat-treatable: 1000, 3000, 4000, 5000.

3. What sort of protecting gasoline ought to I exploit for aluminum welding?

For each Fuel Tungsten Arc Welding (GTAW or TIG) and Fuel Metallic Arc Welding (GMAW or MIG), use pure argon for aluminum supplies as much as ½” in thickness. Above ½” in thickness, operators could add anyplace between 25 to 75 p.c helium to make the arc hotter and enhance weld penetration. Argon is finest as a result of it offers extra cleansing motion for the arc than helium does and it is usually inexpensive than helium.

By no means use any shielding gasoline that incorporates oxygen or carbon dioxide, as this can oxidize the aluminum.

4. For GTAW, what sort of electrode is finest for aluminum?

For many supplies, together with metal, a two-percent thoriated tungsten electrode is really helpful, however since aluminum is welded with AC fairly than DC, {the electrical} traits are totally different and the quantity of vitality put into the tungsten electrode is increased when AC welding. For these causes, pure tungsten or zirconiated tungsten are really helpful for aluminum welding. As well as, the electrode diameter for AC welding must be considerably bigger than when utilizing DC. It’s endorsed to start out with an electrode that’s 1/8″ and alter as wanted. Zirconiated tungsten can carry extra present than pure tungsten electrodes. One other useful trace for AC welding is to make use of a blunt tip — the arc tends to wander round a pointed tip.

5. How a lot preheat ought to I exploit when welding aluminum?

Whereas a bit of preheat is sweet, an excessive amount of preheat can degrade the mechanical properties of the aluminum. As was mentioned earlier, the final warmth therapy for heat-treatable alloys is 400°F, so if the operator preheats the aluminum to 350°F and holds the temperature in that vary whereas welding, the aluminum’s mechanical properties are modified. For the non-heat-treatable alloys such because the 5000 sequence, if the operator holds the temperature even within the 200°F vary, she or he can sensitize the fabric to emphasize corrosion cracking. Most often, some preheat is appropriate to dry the moisture away from the piece, however preheat ought to be restricted.

Due to aluminum’s low melting level — 1200°F in comparison with 2600°F to 2700°F for metal, many operators assume they solely want light-duty tools to weld the aluminum. However, the thermal conductivity of aluminum is 5 occasions that of metal, which implies that the warmth dissipates in a short time. Due to this fact, welding currents and voltages for welding aluminum are increased than they’re for metal, so operators really want heavier-duty tools for aluminum. Many inexperienced aluminum welders use preheat as a crutch. Since tools for welding aluminum must function at increased capacities, many really feel that preheat helps get rid of tools limitations, however this isn’t the case.

6. What’s the correct stress-relieving apply for aluminum welds?

Put up-weld stress reduction will not be really helpful for aluminum. When welding, residual stresses are created across the neighborhood of the weld as a result of the molten materials shrinks because it solidifies. Additional, while you take away materials by machining it tends to distort and create dimensional instability. To keep away from this in metal, operators carry out stress-relieving by heating the fabric sizzling sufficient to permit the atoms to maneuver round.

For metal, the stress-relieving temperature is roughly 1050°F to 1100°F; however for aluminum, the correct stress-relieving temperature is 650°F. Which means that to ensure that post-weld stress reduction on aluminum to be efficient, the fabric should be heated to a temperature the place mechanical properties shall be misplaced. Because of this, post-weld stress reduction will not be really helpful for aluminum.

7. How can I inform totally different aluminum alloys aside?

There are fairly just a few totally different aluminum alloys and for correct and protected welding, you must know what alloy you’re welding. For those who don’t, you’ll be able to comply with these normal pointers:

  • * Extrusions are typically 6000 sequence alloys
  • * Castings most frequently are a mix of aluminum/silicon solid — some are weldable, others are usually not
  • * Items of sheet, plate or bar are in all probability 5000 to 6000 sequence alloys

If you wish to be exact, an alloy tester package that can enable you to decide the precise make-up of your alloy.

8. How do I GTAW weld two dissimilar thicknesses of aluminum?

When an operator has two dissimilar thicknesses, she or he should set the parameters in order that they’re excessive sufficient to weld the thickest piece. When welding, favor the joint and put extra of the warmth on the thicker piece.



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