Refill Friction Stir Spot Welding of Magnesium AZ31B sheets for Superplastic forms

Lance Hanson SDSM&TFaculty Advisors: Dr. C. Widener, Dr. M. West, Dr. B. Jasthi, T. Curtis

Introduction Approach Results

Conclusions• The data supports the conclusion that as the Weld penetration

into the 2nd sheet increase the peak load of the weld increases. This also leads to an increase peak load of the sticking bond between the 2nd and 3rd sheet.

• The data also supports that cleaning the 2nd and 3rd sheet prior to welding will increase the bond strength their by increasing the peak load.

Acknowledgements: This work was made possible by the National Science Foundation I/UCRC Center for Friction Stir Processing and REU Back to the Future Site DMR-1157074, Pacific Northwest National Laboratories.

• Refill Friction stir spot welding (RFSSW) is a newly developed solid state welding technique.

• Refill Friction stir spot welding is a method of Friction Stir Spot Welding (FSSW) where extruded material from the plunge is captured and used to fill in the void called the keyhole.

• Perfect for use with Aluminum, Magnesium and high strength steel where avoidance of rapid cooling is desired.

• Used with materials that are difficult to weld with traditional welding methods such as Resistance spot weld.

• In these experiments, Magnesium AZ31B sheets were spot welded together via Refill friction stir spot weld for the purpose of forming Superplastic Structures

Background

Broader Impact• Main goal is create a spot weld suited for Superplastic Forming.• These structures will have a variety of uses from:

• Creating Safer automobiles• More efficient Cooling systems• Economical product design

• Attractive process because it has no consumable parts and requires less energy per weld then conventional welding

• Using material provided by PNNL, examine the feasibility of welding 2.25 mm thick sheets to 1 mm thick AZ31B sheets.

• Welds made using a sleeve/shoulder plunge appose to the pin plunge to increase surface area and strength of weld. (Figure 1)

• Test different depths of penetration into the middle sheet of a 3 sheet pack.

• A three sheet pack consists of a top sheet 2.25 mm thick, a middle sheet 1mm thick, and a Bottom sheet 2.25 mm thick(see figure 4)

• Examine microstructure of welds for parameters sufficient for Superplastic forming of Structures

• Use Single Lap shear tensile tests to examine the peak loads that the weld bond (figure 2) and the bond created between 2nd and 3rd sheet during the weld process, if one exists. (Figure 3)

• Analyze results with SEM and Macrographs.• Take best results and create welded sheet packs for superplastic

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Peak

load

lbf

% penetration 2nd sheet

Shoulder Clamp

Figure 1: Refill Friction Stir Spot Welder Process (RFSSW)

Image of SDSMT RFSSW

Image of MTS tensile tester and test coupon

Figure 2: Coupon diagram for 1st /2nd sheet weld test

Section view of coupon weld test

Figure 3 : Coupon diagram for 2nd/3rd sheet bond peak load test

Cross section view of bond peak load test

Graph 1: Lap Shear Tensile test of 1st and 2nd sheet. Material was welded without any prior cleaning

Graph 2: Lap Shear Tensile test of 2nd and 3rd sheet. Material was welded without prior cleaning

Graph 3: Lap Shear Tensile test of 2nd and 3rd sheet. Material was welded after removing surface oxidation.

Figure 4: Upper image shows spot weld placement for 3 sheet pack. Right image shows Superplastic Structure of welded sheet pack.