PSI - Issue 17

Liting Shi et al. / Procedia Structural Integrity 17 (2019) 355–362 Liting Shi/ Structural Integrity Procedia 00 (2019) 000 – 000

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realized that they could not directly measure shear strength of the weld nugget or HAZ. Instead, they used microhardness in their predictions. More recently, Shi et al. (2019) developed a new formula to determine critical nugget size in aluminum RSWs using directly measured shear strength of weld nugget and HAZ. In the present study, we further extend our study to calculate a critical aluminum-steel weld nugget diameter based upon experimental results. The calculated critical weld nugget diameters were then compared with experimental results to predict fracture modes for aluminum-steel stack-ups having different sheet thicknesses.

2. Materials and experimental procedures

The materials used in the present study were 0.8-mm thick X626-T4 aluminum alloy, 1.2-mm thick AA6022-T4 aluminum alloy, as well as 0.9-mm and 1.2-mm thick hot dipped galvanized (HDG) low carbon steel (LCS) sheets. The chemical compositions (in wt%) of these materials are provided in Table 1

Table 1 Chemical composition of X626-T4, AA6022-T4 aluminum alloy and LCS (in wt %). Materials C Cr Ti Mg Cu Mn Si

Al

Fe

X626

- -

- -

- -

0.47

0.055 0.240

- -

0.670 0.750

Bal. Bal.

0.120 0.170

AA6022

0.510

0.9mm LCS 1.2mm LCS

0.032

0.040

0.063

-

0.033

0.120

0.013

0.089

Bal.

0.045

0.019

0.001

-

0.007

0.217

0.012

0.038

Bal.

Tensile shear specimens were made for two types of aluminum stack- ups using GM’s MRD electrode and CSS schedule and two types of aluminum-steel RSWs using the MRD and multiple-solidification weld template developed by Sigler et al. (2017), (2015). The sketch of the tensile shear specimen is illustrated in Fig. 2 while the welding schedules are provided in Table 2. After welding, all specimens were baked in an oven at 175°C for 35 minutes to simulate the thermal bake operation used in production to cure adhesives and coatings.

Fig. 2 Sketch of tensile shear specimen.