ARC MAGAZINE

How To Avoid Solidification Cracks in 60-Series Aluminum Alloys

One of the most widely used families of aluminum alloys is from the wrought aluminum-magnesium-silicon class, commonly referred to as 60- or 6xxx series. The key to a successful weld of this series is to change the chemistry of the weld deposit by adding an adequate amount of filler metal of a different composition. This will make the weld less crack-sensitive.

For good reason, there is no 60-series of filler metals – all the welds would crack. While the chemistry of 60-series alloys gives them their heat treatability and strength, it also makes them sensitive to solidification cracks.

So, fabricators utilizing the 60-series should use such filler metals as those from the aluminum-silicon (40- or 4xxx) and aluminum-magnesium (50- or 5xxx) series.

The 60-series of aluminum alloys is predominantly used as extrusions, as well as for rolled sheet and plate. The alloys are versatile, heat treatable to moderately high strengths, formable and more corrosion-resistant than other families of heat-treatable alloys. Extruded products from the 60-series are a leading choice for architectural and structural applications. The most common alloy in the series, 6061, is often used to fabricate truck and marine frames.

Tee, lap, corner and edge joints can all be successfully welded without beveling, as long as adequate filler is added. The weld deposit is a mixture of the filler metal and base metal, and it should contain more filler metal than base metal. Fabricators should avoid excess dilution of the weld with the base metal on lap and corner joints.

Preparing butt joints by beveling will help ensure that adequate filler metal is added. Square full penetration butt joints should be avoided as too much base metal will be diluted into the weld causing the weld deposit to be crack sensitive. Moreover, concave craters must be avoided at the end of the weld to prevent crater cracks.

ER 4043 and ER 5356 are the most common filler metals selected for welding 60-series aluminum. Service conditions will determine which of the two, or a different alloy, is the correct choice. It’s best to consult filler metal selection charts to determine the correct application.

Tools

• 6061-T6 aluminum tube, 0.125-inch wall thickness, approximately 60-degree included angle bevel
• Lincoln Electric Square Wave TIG® 200
• Lincoln Electric® ER4043 filler wire, 3/32-inch diameter
• Argon gas
• Standard 3/32-inch collet body
• 150 amp, flex head torch

Personal Protective Equipment

• Long-sleeved, fire-retardant clothing
• Lincoln Electric Red Line™ TIG welding gloves
• Helmet
• ANSI-approved safety glasses with side shields
• Well-ventilated area (preferably with high ceiling)

PREHEAT SAFELY

We always want to make sure we’re working safely when welding and working with torches. Refer to ANSI Z49.1: “Safety in Welding, Cutting, and Allied Processes,” which includes heating.

Make sure to wear the proper safety gear, including flame-retardant clothing, gloves and proper safety glasses. Make sure your jeans or pants are not frayed.

For proper torch setup and application, refer to the manufacturer’s guidelines. Make sure to have the correct check valves on the torch, flash arresters back at the regulator, hoses in good condition, and regulators set and operating properly.