What is 6061-T6 Aluminum?
Aluminum grade 6061 is a aluminum alloyed with Silicon & Magnesium as main alloying element. The UNS Number of Grade 6061 is A96061. The P Number as per ASME Section IX for 6061 aluminum is P No. 23. The alloy is used in general aluminum structure, railway parts and aerospace applications.
The below diagram gives an overview of general aluminum alloys.
Classification of aluminum grades
The aluminum alloys have a naming system that has a high level of international recognition. It has a four-digit base:
Pure alloys: 1xxx
Aluminum- copper alloys 2xxx
Aluminum -manganese alloys 3xxx
Aluminum – silicon alloys 4xxx
Aluminum – magnesium alloys 5xxx
Aluminum – magnesium- silicon alloys 6xxx
Aluminum – zinc alloys 7xxx
What are the Chemical properties of 6061-T6 aluminum?
The chemical composition of Al 6061 material as per the material specification is given in the below table for reference.
|95.85 – 98.56||0.8 – 1.2||0.40 – 0.8||0.0 – 0.7||0.15 – 0.40||0.04 – 0.35||0.0 – 0.25||0.0 – 0.25||0.0 – 0.15||0.05 each, 0.15 total|
Physical properties of 6061-T6 aluminum
The physical properties of 6061 alloy that affects the weldability of aluminum are density, its melting points and thermal expansion are given in the table for reference.
|Melting Point||650 °C|
|Thermal Expansion||23.4 x10^-6 /K|
Properties as per the Spec: BS EN 755-2:2008
|Proof Stress||240 Min MPa|
|Tensile Strength||260 Min MPa|
|Hardness Brinell||95 HB|
TIG/ MIG Filler wire for 6061-T6 Welding
Aluminum grade 6061-T6 is welded using ER5356 & ER4043 and both filler wires can be used to weld Aluminum 6061 grade.
1. ER4043 (GTAW/GMAW) – ER4043 is silicon alloyed (5%) aluminum TIG wire used for welding of 6061 grade. The wire offers very good weld fluidity with a good weld appearance. ER4043 is not used for welding applications where the weld is subjected to high shear stresses. It is having lower shear strength than the ER5356 filler wire. ER4043 is used with pure argon shielding gas & Alternating current (AC) and pulsed current polarity for TIG & MIG welding applications. The AWS specification for ER4043 is AWS A5.10. F-Number of ER4.43 is 23.
ER5356 (GTAW/GMAW) – ER5356 filler wire offers good strength and weld ductility compared to ER4043 type. ER5356 is a widely used TIG/MIG filler rod and has many uses. It can be used with DC Reversed Polarity and pure Argon shielding gas to be used for shielding purposes. F-Number of ER5356 is 22.
Selection of welding consumables for Aluminum Welding
The best filler rod for TIG or MIG welding of 6061 aluminum is RR5356 and ER4043. Also, you can use this chart to find the best suitable GTAW/ GMAW filler wire to weld the various grades of the Aluminum.
Hot cracking can be prevented by using 4043 type filler wire, but it will give lower ductility and toughness compared to 5356 type wire. 4043 types due to high silicon content give the poor color match to 5XXX and 6XXX aluminum base metals after anodic oxidation treatment.
When welding 5XXX (high Mg, more than 3% usually), 4043 is a poor choice as it will make an intermetallic compound of mg2Si in the weld metal. This will lower the weld metal ductility and increase its crack sensitivity.
Which Welding process is best for 6061 aluminum welding?
Aluminum can be welded with TIG and MIG welding easily. GTAW or TIG welding is used for welding sheet metal and thin parts using AC polarity along with pulse current. AC welding gives cleaning action in the welding arc that helps to automatically clean the oxide layer from the aluminum surface. MIG welding is used for welding of heavy thickness. More advanced welding processes such as friction stir welding and laser welding are used a lot in the aerospace applications and other aluminum welding applications.
TIG Aluminum Welding Parameters
MIG Aluminum Welding Parameters
Shielding and Backing Gases for Aluminum welding
Pure Argon is widely used. Argon-Helium mixture in TIG/ MIG welding. Helium addition helps for a better weld formation and increases the welding speed. Helium also minimizes the risk of pores and lack of fusion. Pure helium is not used due to the high Ionisation potential of the gas as well as the high cost of the gas.
The gases used for shielding of AL6061 are argon, helium, or a mixture of the two. Both provide sufficient oxidation protection. The choice depends on which of the various gas properties are required for the best weld. The significant properties are:
Density: The lighter gas is more likely to be blown away
Ionization Potential: The gas
Thermal conductivity: The gas with the higher thermal conductivity gives the widest weld bead (due to conductivity over the surface)
Cost: Helium has to be imported and is expensive. Argon is extracted from the air by normal liquefaction processes.
The gas must also be free of moisture and hydrogen. The most usual gas is an argon-helium mixture.
Preheat for welding of 6061 aluminum is recommended for thicker sections or whenever sufficient penetration can not be achieved due to the high thermal conductivity of the aluminum.
So, if any of the above issues are faced, a preheat temperature of 150 to 200°C can be applied. Also, when repairing 5XXX (Al-Mg) grades, it can crack in the weld or HAZ area. Following a preheat in these conditions is very beneficial to mitigate the cracking inter-alia by using the right filler wire.
Watch our YouTube video to Learn what is Preheat, Inter-pass & post-heating.
Usually, the interpass temperature is kept above the minimum preheat temperature when welding 6061 aluminum.
Weldability of Aluminum Alloys
Weldability is the combined effect of many variables. These relate to:
- The difficulty of melting: Factors concerned are: melting point, heat capacity, heat radiation effect, and thermal conductivity effects
- Distortion problems: These are influenced by thermal expansion and thermal conductivity inter-relations. The possibility of phase changes that can give other density changes must also be considered
- Chemical reactions: The predominant problems here are the effect of oxidation and the possibility of a gas solution. With aluminum, the residual oxide film can also give problems
- Cracking tendency. Some alloys have a particular tendency to crack and special attention has to be paid to minimizing this.
Cracking in 6061 Aluminum grade
Cracking in 6061 aluminum can be solidification cracking in the fusion zone or liquation cracking. To avoid cracking in aluminum welding of 6061 or other grade use:
- Use proper filler wires and dilution.
- Use less susceptible alloys.
- Use a wide weld bead and/or arc oscillation.
- Use low heat input.