Introduction

Aluminum base metals are classified in two ways: as wrought alloys produced by mechanical working such as rolling, extruding, or forging, or cast alloys produced by pouring into a mold. Wrought alloys are further divided as either heat treatable or non-heat treatable depending on the composition.

• Wrought alloys - produced by mechanical working such as rolling, extruding, or forging
• Heat-treatable
• Non Heat-treatable
• Cast alloys - produced by pouring into a mold

Below is a basic step by step guide to follow when welding aluminum.

Safety First

Select Joint Design and Fit up

Start by determining the best manner in which to join your base metals. Correct joint design and fit up are critical steps to insuring a strong bond upon weld completion. Be sure to consider the degree of strength required, welding position, metal thickness and joint accessibility.

The five basic types of joints are butt, corner, edge, lap and tee. These five joints can be arranged in many combinations to create a large variety of welds. Fixtures and jigs are helpful in securing the work pieces in place during the joining procedure. Sheet metal and most fillet and lap joints should be clamped tightly over the entire length of the work.

Choose the Welding Process

The most popular processes are Gas Metal Arc Welding (GMAW), sometimes called MIG welding and Gas Tungsten Arc Welding (GTAW) sometimes referred to as TIG welding. A third process, Shielded Metal Arc Welding (SMAW) or stick welding, has limited use on aluminum and is used primarily for small repair jobs on material 1/8" or more thick.

• SMAW - Shielded Metal Arc Welding or Stick Electrode
  

  SMAW is an electric arc welding process in which heat for welding is generated by an electric arc between a covered metal electrode and the base metal. The electrode coating provides shielding. The welding equipment for this process is currently the most inexpensive of the methods described here. However, electrodes do create some inefficiency, such as stub loss and a slag coating, which must be removed.

• GTAW - Gas Tungsten Arc Welding or Tig Welding
  

  Tig Welding is easily performed on a variety of metals. It generally requires little or no post weld finishing. It is an electric welding process in which heat for welding is generated by an electric arc between the end of a non-consumable tungsten electrode and the base metal. Filler metal may be added, if necessary. An inert shielding gas supplies shielding for the arc. (Inert gas creates a protective atmosphere around the welding in process.)

• GMAW - Gas Metal Arc Welding or Mig Welding
  

  Gas metal arc welding is quick and easy on thin-gauge metal as well as heavy plate. It generally calls for little post weld cleanup. GMAW is an electric arc welding process where heat is produced by an arc between a continuously fed filler metal electrode and the base metal. Shielding is obtained from an externally supplied gas or gas mixture. The two most common types of GMAW are:

• Short Circuit Transfer - The arc is broken or short-circuited with each drop of metal and restarted. Short circuiting transfer is not used with aluminum welding.
• Spray Transfer - Metal is transferred across the arc creating a continuous spray of fine droplets of metal. These droplets are projected down to the base metal.

Determine the Appropriate Inert Shielding Gas

GTAW - Argon is suggested for thicknesses up to approximately 1/2". For thicker sections, argon-helium mixtures or pure helium may be used. Pure helium may also be employed for deeper penetration.

GMAW - Argon is used for most applications. It provides deeper penetration and clean welds. Argon-helium mixtures of 25% Ar/75% He are helpful for thicker material (over 0.5 inch). Helium produces a hotter arc which is sometimes necessary due to aluminum’s high thermal conductivity. It also produces a wider weld fusion shape.

See Shielding Gas Guide for further details

Select the Applicable Filler Metal

Filler metal is based on several factors. One consideration is the ability to provide suitable mechanical properties for heat treatable and non-heat treatable base metals, both wrought and cast. Other important factors are freedom from cracking, service conditions, and weld color after anodizing.

Set the Parameters

DC uses either straight polarity, which is electrode negative or reverse polarity, which is electrode positive. Direct current flows in one direction continuously through the welding circuit. There are several advantages of DC. It works well at low current settings and with small diameters. In addition, igniting the arc and maintaining a short arc is easier.

AL-43 Aluminum Electrode is used with DC-reverse polarity.

Current Amperage recommended settings are:

GTAW - Manual GTAW of aluminum is usually done using alternating current (AC). A high frequency generator is employed for arc starting and stabilization. Pure or zirconiated tungsten electrodes are used for AC welding. Tungsten electrodes should be prepared with a hemispherical-shaped tip.

The parameters for manual GTAW are dependent upon plate thickness, weld position and joint design. The following settings should be helpful in establishing a procedure. Settings are for the flat position.

GMAW - Gas metal arc aluminum welding is done using DC reverse polarity (electrode positive.) Filler metal transfer is in the spray mode. Suggested settings for flat position manual GMAW (argon shielding gas) are:

Clean the Base Metal

Cleaning should be done just prior to welding to prevent the formation of oxides. The base metal surface must be free of grease, oil, paint, dirt, etc. A clean surface will provide a smoother, stronger joint. Brush the plate surface and edges with a stainless steel wire brush to remove burrs and oxides. Gloves should be worn to prevent hand oil or dirt from getting on the joining surface.

Preheat if Applicable

Preheat is generally unnecessary in aluminum welding. In some cases it can be helpful when welding casting to reduce cracking tendency. It may also be useful to equalize weld penetration when welding metals of different thicknesses.

Welding Technique

A good welding technique is developed as a welder gains experience. The following are basic welding tips:

• Use fixtures and/or jigs to help keep work in place.
• Joints should be designed to provide suitable access and to promote weld penetration.
• Insure adequate shielding by centering the filler metal in the gas and weld puddle area.
• For GMAW use a forehand welding technique (gun pointed in the travel direction).
• In GTAW filler metal should be dipped into the weld puddle, but should not drip into it.
• Move the torch/gun along the joint at a steady, constant speed to maintain uniformity.
• Hold the torch/gun over the weld until gas stops to keep work protected.
  

Cooling / Post Weld Cleaning

Allow the joint to cool slowly. If AL-43 coated electrodes are used, remove slag after welding.

Troubleshooting

Please consult our Frequently Asked Questions.

Aufhauser Filler Metals

Aufhauser manufactures a complete line of filler metals for aluminum welding. Based on application, we help you choose an appropriate aluminum welding alloy from our Selection Chart.