Aluminum wheels: to weld or not to weld?

Introduction

Subject the use of welding in the repair of automotive aluminum discs is highly relevant. The popular forum site chipmeyker - Site for craftsmen working with metal, amateurs and professionals, such a discussion has been simmering for nearly 8 years (Welding wheels). Similar discussions are also in overseas forums.

Below we present information, which explains the features and difficulties of repair welding of aluminum rims:

  • regulations;
  • wheel rim manufacturing technologies;
  • aluminum alloys, which are used in rims;
  • heat treatment, which applies to aluminum rims;
  • welding methods, which are used when welding aluminum rims;
  • heat affected zone during welding aluminum.

This information is not intended to be a complete statement of the topic under discussion and not an instruction for welding aluminum wheels.

terms

The Russian-language technical literature, especially in the network usually uses the term "wheels". In the English regulatory and technical literature wheels called «wheels», ie - "the wheel". Each wheel has a rim, ie that part of the, on which the tire is mounted. "Disco" is called a wheel element, which connects the rim to the vehicle axle. Steel wheels of trucks do not usually have a hub, and are attached to the axis directly through the disk. Therefore they are called «disk wheels» – "Disc wheels" [1, 2]. Aluminum wheels are often instead of the disc are "spokes", which pass into the "hub". The hub is attached to the vehicle axle. note, that GOST R 50511-93 [3] uses international terms "wheels" and "disc wheels".

Below, in order to avoid confusion, we will interchangeably use the terms "wheel", "Disc wheel" and "wheels".

Foreign regulations

Wheels are heavy duty vehicle components, of which largely depends on its safety. That's why leading automobile manufacturers and the wheels are not allowed to perform them any repairs, including repair welding.

Standard ISO 14400 clearly indicates, that the repair welding wheel drive should not be made, since this can introduce additional stresses in its critical regions [1]. The organization EUWA (Association of European Wheel Manufactures) - the Association of European manufacturers of automobile wheels - strictly prohibits the repair of damaged rims and rims of automobile wheels using heating, welding or adding any additional material [4].

At the same time, the regional regulation of the Canadian province of British Columbia - rules for the repair by welding of aluminum rims - allows limited use of welding for repairing rims of wheels [5].

Welding aluminum wheels: Canadian regulations

Some provisions of the Canadian Rules, which may be of interest to specialists in welding aluminum rims [3]:

  • The minimum thickness of the aluminum disc element material, which can be repaired by welding, is 1,5 mm.
  • Repair shop must always have an insurance fund specifically for the repair of aluminum disks at a rate of not less than 2 million dollars (you have to understand, Canadian).
  • The workshop must have welding machine for at least 250 ampere.
  • The workshop must have a weld repair supervisor, who has experience in welding aluminum not less than 5 years.
  • This master is responsible for:
    a) the decision to repair the disk by welding or send it to scrap;
    b) repair method for each repaired aluminum disc;
    c) the quality of welding of the repaired aluminum disc.
  • In the workshop for repair of aluminum wheels a special register shall be kept, which records information about each repair aluminum wheels.
  • Each welder must pass on the knowledge exam test methods and acceptance criteria welding repair aluminum wheels.
  • repair workshop aluminum wheel rims should just pass the certification audit in two years, to confirm, that it has the appropriate equipment, qualified repairmen and skilled welder welding.
  • Authorized structural welding repair limited rim, as shown in Figures 1 and 2.
  • Redecorating is permitted around the wheel, including repair welding surface dents and projections, which do not affect the structural integrity of the wheel.
  • Allowed repair disks, which applies a weld in combination with the limited hot and cold straightening.
  • hot leveler temperature should not be higher 204 °C (400 °F).
  • Repair welding must be performed only with the use of approved modes and materials TIG welding or by MIG.
  • Welding may be carried on wheel rims made of aluminum casting alloys and wrought alloys 5xxx and 6xxx series.
  • Acceptability of aluminum welds must be in accordance with Canadian regulations for welding aluminum structures.

Figure 1 - Basic elements of a typical wheel rim [3]


Figure 2 - Enabling or disabling a weld zone
typical wheel rim [3]

The main types of aluminum rims

The one-piece cast drive

This is the most widespread type of aluminum wheels. The proportion of solid - solid - alloy wheels in the total number of aluminum wheels to 2012 year was: 80 % in Europe, 85 % – in the US and 93 % – in Japan [6].

Two-piece disc (sheet metal rim + cast trap)

The front part of the disc - hub - are manufactured by casting, the rim is obtained by rolling or extrusion [2]. These two parts are connected to each other by bolts, steel or titanium. The starting sheet - made of aluminum-magnesium alloy, typically alloy 5454 [2, 3]

Two-piece disc (sheet rim and hub)

The rim and hub are made by metal forming methods - hot or cold: deep upsetting, rolling, punching, forging, etc.. P. Both parts are connected by welding. The starting sheet - made of aluminum-magnesium alloys, mostly of an alloy 5454 [2]

Disc three parts

Hub and spokes of a complex shape is injection. The rim consists of two halves, which is manufactured by rolling or extrusion. The rim is bolted or welded to the hub [2].

One-piece disc: casting + katanıy Zimbabwe

This process combines the casting technology with metal forming methods for forming the rim, hot or cold.

forged wheels

mechanical specifications forged wheels They are the highest of all types, on the market. They are obtained by machining the forged billet of aluminum alloy 6061 and 6082.

Drive from the preform in a semi-solid state

This type of drive is not very common because of their limited production. Their mechanical properties are similar to those of forged wheels. In the semi-solid cast rolled rim techniques or metal forming the central part of the disc, which is bolted or welded to the rim [2].

Aluminum alloys for automotive drives

Aluminum casting alloy

Alloy wheels are made of casting aluminum alloy flint with a silicon content of 7 by 12 %.

In the USA and Japan are used almost exclusively AlSi7Mg0,3 aluminum alloy is thermally hardened state T6. This alloy has a nominal silicon content 7 % and magnesium - 0,3 %. In the US, a similar alloy is designated A356.0.

AlSi7Mg0,3 same alloy used in Europe, wherein both thermal hardening, and without thermal hardening. In Germany and Italy, the alloy AlSi11Mg is used (nominal silicon content 11 %, magnesium - 1 %), usually without heat hardening [6].

Table 1 - Casting aluminum alloys,
used in the rims

Wrought Aluminum Alloys

One-piece forged wheels are made from the following wrought aluminum alloys:

  • 6082 (in Europe)
  • 6061 (in USA);

alloys 6082 and 6061 refer to the 6xxx series. The main alloying elements are magnesium and silicon (nominal contents - up to 1 %). Are thermally hardening.

aluminum sheet, which is used in the manufacture of wheels, typically consists of an aluminum alloy 5454. Alloy 5454 It refers to the 5xxx series. The major alloying element is magnesium nominal content 3 %. Is thermally neuprochnyaemym. Increased strength can be achieved by cold plastic deformation - autofrettage.

Table 2 - Wrought aluminum alloys,
used in the rims

Tempers of aluminum alloys

Forged aluminum wheels from wrought alloys 6082 and 6061 hardened by quenching and artificial aging (condition T6).

Alloy wheels or their elements made of AlSi7Mg0.3 alloy can be thermally hardened by quenching and artificial aging (condition T6) or used without heat hardening, that is, in a cast state (state F).

Alloy wheels made of AlSi11Mg alloy are usually not subjected to heat hardening (state F) [2, 6].

Thermally neuprochnyaemye 5xxx series alloys may receive in the manufacture or repair of cold-worked condition, which are designated Hhh.

Heat-affected zone when welding aluminum

Welding Metallurgy fusion

at arc welding of aluminum in the weld melts in the weld zone of the base metal, and a filler material, if applicable. During solidification of these metals there are new grain, that "grow" in the parent metal grain, who did not have heat, to melt [7].

Regardless of the type of heat source, All welds in fusion welding have areas with different microstructures abruptly. These changes in the microstructure occur due to phase transformations in the solid state, such as:

  • recrystallization and / or grain growth in cold-worked materials;
  • overaging or dissolution of the hardening phase in thermally hardened (aged) materials.

This zone with a changed microstructure is called the heat-affected zone of welding [7].

strength aluminum welding heat-affected zone

Aluminum alloys in the cast state (F state) or annealed state (O state) can be welded without any significant loss of strength in the weld HAZ. In this case, the weld strength corresponding to the strength of the base metal. It belongs, for example, to cast rims and AlSi11Mg alloy AlSi7Mg0,3, which are not subjected to thermal hardening.

If aluminum alloy, for example, received its increased strength due to cold plastic deformation (autofrettage) or due to the release of hardening particles (aging), for example, able to T6, then the heat-affected zone can be a significant loss of strength.

work-hardened alloys, for example, 5xxx series alloys, lose strength due to the recrystallization process, which occurs in the heat affected zone at a temperature above 200 oC, and at a temperature above 300 ºС - partial or complete annealing (figure 3).

Figure 3 - The mechanical properties of cold-worked alloy series 5xxx
in the heat affected zone of welding [7]

Thermally strengthened alloys when heated lose strength due to the additional allocation and consolidation of reinforcing particles. This process is called overaging. At temperatures above 300 ºС the state of partial or complete annealing is achieved (figure 4).

Figure 4 – The mechanical properties of the alloy is thermally hardened 6061
in the heat affected zone of welding [7]

alloys 6061, 6082, 5454 and A356.0

Thermally hardened alloy 6061 T6 state has a minimum yield strength and durability 240 and 290 MPa, respectively. The heat-affected zone may be reduced to 115 MPa (48 %) and 175 MPa (60 %) [8].

Thermally hardened alloy 6082 T6 state has a minimum yield strength and durability 255 and 300 MPa, respectively. The heat-affected zone may be reduced to 125 (49 %) and 185 MPa (62 %) [8].

Cold-worked state to H24 / N34 Alloy 5454 It has minimal yield stress and strength 200 and 270 MPa, respectively. In the heat affected zone, these values ​​can be reduced to 105 (53 %) and 215 MPa (80 %), that is, almost to the strength properties of the annealed state [8].

Alloy A356.0 (AlSi7Mg0.3), when cast into permanent molds, has minimum yield and strength limits in the T6 state 200 and 250 MPa, respectively. In the welding heat-affected zone T6 state moves to state F with a minimum yield strength and strength 90 MPa (45 %) and 180 MPa (72 %) [9].

conclusion

When deciding on the application of repair welding aluminum wheels should be taken into account, in the HAZ of welding, mechanical properties of the base metal may be reduced.

For the purpose of a wheel disk and changes the mode of welding necessary, least, know:

  • the chemical composition of the aluminum alloy;
  • aluminum alloy condition (cast condition, thermally hardened state, cold-worked condition).

Sources:

  1. ISO 14400:2015
  2. Aluminium&Cars. Design, technology, innovation – Edimet, 2005
  3. GOST R 50511-93
  4. http://www.euwa.org/safety-informations/es-standards
  5. http://www.bclaws.ca/civix/document/id/loo94/loo94/5_97
  6. https://www.engineeringclicks.com/aluminium-car-wheels – 2012
  7. The welding of aluminium and its alloys /Gene Mathers – 2002
  8. EN 1999-1-1: 2007 (Eurocode 9)
  9. https://www.foundry-planet.com/fileadmin/redakteur/Material/08-03-10-Leporello_engl.pdf