New developments in Laser Welded Blanks using AlSi coated Boron Steel

• Conclusions

Before laser-welding, the Aluminum-Silicon coating near the edge is partially removed in both sides by using a laser ablation process (ArcelorMittal patented process)
− The top layer is removed to avoid excessive Al dilution in the weld
− The intermetallic layer is intentionally kept to help with corrosion protection and avoid decarburization

AM patented partial ablation process is today the only safe way to reach less than 0.3% of Aluminum content in the weld for AlSi-1500 - AlSi-1500 laser welded assembly.
To reach 1.2% however other processes may be acceptable

Cost & processing efficiency
− Reduction in capital
− Less processing steps
− Filler wire a key enabler
− Potential for cost saving

 Mechanical tests on coupons:
1. Estimate weld strength - static tensile test
2. Assess the dynamic effect on weld behavior - dynamic tensile test
3. Determine the ability of a weld to be plastically deformed and
absorb energy – Fracture test

 Mechanical testing on stamped Omega shape :
4. Estimate the effect of complex loading on
Omega part
 Mechanical testing on automotive parts:
5. Estimate the effect of complex loading on
real parts

• Dynamic loading, weld with Aluminum content

• Maximum Aluminum Content (MAC) for avoiding δ-ferrite formation at high temperature

For pure Iron-Al mixing :

• Inter-metallics (AlFe) are formed when Aluminum content is higher than about 20 at.% (about 10 wt.%)

• δ-ferrite is created at high temperature from the liquid state when Aluminum content is higher than about 0.7 wt.%

• Several criteria are necessary to ensure that the weld is not the weak point:
 Weld Strength intermediary between AlSi-1500 and AlSi-500
 No δ-ferrite grains for avoiding the risk of brittle fracture

• Aluminum content measurements require careful protocol and specific equipment (SEM, EDS with special methodology) to reach required accuracy for low value (close to 1%).
• Dynamic tensile test and component testing are long and sometimes difficult to implement
• ArcelorMittal is developing a new dynamic fracture test to expedite results

Filler wire is key ingredient to the process and it improves robustness in 3 ways:
1. Weld geometry control (gap bridging)
2. Aluminum dilution
3. Gamma stabilizer (C, N) element increase in

molten area:
Introduction of some elements like Carbon can counter balance Aluminum effect on weld quench ability.

• ArcelorMittal is global leader in advancing hot stamped laser welding process.
• Our standard partial ablation process is the proven way in industry to meet weld seam requirements for all hot stamped combinations (AlSi-1500+AlSi-1500, AlSi-1500+AlSi- 500).
• New industrial process with reduced ablation and filler wire is robust and in production for AlSi-1500+ AlSi-500 combinations.
• However, this new process bears new risk which requires  dynamic validation:
− The key point is to avoid δ-ferrite grains created during the welding from the liquid state. That needs to have an average Al% below 1.2 % wt.
− Low alloy filler wire mainly acts by a dilution effect
• Welding process with one side ablation in combination with filler wire addition is a good compromise between industrial production constraints and weld performance.
• ArcelorMittal continues to research ways for improving product robustness and save time in the development of new product and processes.