Case history: ADI-steel suspension arm

Example welded joint between austempered ductile iron (EN-JS-1050) and structural steel (42CrMo4 Q&T)

This case history describes a suspension arm obtained by welding austempered spheroidal cast iron (EN-JS-1050) and structural steel (42CrMo4 Q&T) for our customer Streparava. This type of suspension arm is generally used for vehicles of the automotive sector and, in particular, it is a key element in the front suspension system.

Application features and advantages of the ADI-steel hybrid suspension arm

This suspension arm is considered hybrid due to the dissimilar welded joint between two different materials which are not typically welded together. In fact, a 42CrMo4+Q&T steel pin was welded to the ADI1050 arm, which was necessary to anchor the suspension system to the chassis of a high-end Top Car.

The end customer was open to the possibility of changing technology and production process in order to achieve, first of all, a reduction in costs, which were previously high due to a complex supply chain and due to the complexity of obtaining the particular shape of the component by forging. The customer also aimed to obtain a lighter component to reduce its impact in terms of consumption and emissions, while having the same structural requirements.

In addition to the advantages described above, the ADI-steel hybrid solution also met the safety requirements for this type of application.

The starting component was a monolithic forged and machined 38MnVS6 steel element. Thanks to the development of the welding process by Italian Institute of Welding of Genoa, together with the test campaign carried out by University of Padua, it was possible to define new design tools suitable for the production of a new ADI-steel hybrid suspension arm(figure 1).

Braccio fuso in EN-JS/1050-6 EN-1564 | EN-JS/1050-6 EN-1564 cast arm | Arm gegossen aus EN-JS/1050-6 EN-1564

Figure 1

Starting material 38MnVS6+Q&T for forged solution

Material

Rp0,2

Fatigue limit
σAG; PS50%

38MnVS6

550 MPa

850 MPa

&lt 30

≈380

Separated cast sample – In accordance with DIN EN 10267

New hybrid welded solution cast in EN-JS/1050-6 cast iron and 42CrMo4 Q&T forged pin

Material

Rp0,2

Fatigue limit
σAG; PS50%

EN-JS/1050-6 EN-1564

700 MPa

1050 MPa

320-380

440

42CrMo4 Q&T UNI-EN-10083

650 MPa

900-1100 MPa

12%

≈300

430

Separated cast sample – Thickness &lt 30mm

The advantages of ADI austempered ductile iron for a suspension arm intended for the automotive sector

The use of austempered spheroidal cast iron made it possible to produce more complex and net-to-shape geometries than those of the forged original, thus minimizing the excess of material, in relation to the available design volumes (net-to-shape, typical characteristic of cast iron castings.), while also making “windows” to make the structure lighter thanks to the advantages of cast iron casting process.

Figure 2

Considering also the lower specific weight of cast iron (about 10% lower than that of steel), the component achieved an intrinsic weight reduction for the same load requirements, which resulted in an overall weight saving of 1.5 kg from the previous 12 kg to the new 10.5 kg.

The only item still made of steel for safety reasons is the pin that anchors the arm to the chassis.

The ADI-steel hybrid solution has passed all the bench tests required for component validation.

To date, the prototype version used for the technological feasibility test has involved 4 partners; the standard version could potentially involve only Zanardi Fonderie S.p.A. and Streparava.

Comparison between steel and cast iron: the combination of skills for the hybrid suspension arm prototype

For the production of hybrid ADI-steel suspension arm prototypes, Fonderie Baraldi s.r.l., based in Montagnana, has been involved since the beginning for pouring the as-cast component.

Prototypes were then subjected to austempering treatment to obtain the ADI grade required by Zanardi Fonderie S.p.A.

Then, the customer and owner of the design Streparava S.p.A., owner of the design, carried out all machining phase required and the fitting of the pin, with the proper interference, inside the pin-seat obtained on the arm itself, as well as all the subsequent mechanical fatigue tests required for the component approval.

Finally, Costruzioni Generali s.r.l., after the tuning of welding parameters shown in table 2, made the partial penetration fillet-welded joint to guarantee a redundant safe connection between the two components.