Microstructure and Mechanical Property Improvement in Laser-Welded TC4 Titanium Alloy and 301L Stainless Steel Joints Without Filler Metal

Abstract

Pulsed laser welding of Ti alloy to stainless steel (SS) has been applied without filler metal. When the laser beam was focused on the Ti alloy–SS interface, large volumes of Ti-Fe intermetallics were formed in the joint. These Ti-Fe intermetallics were highly brittle, causing the joint to crack spontaneously after welding. The brittle coarse Ti-Fe intermetallics seriously deteriorates the joint strength of Ti alloy and SS; therefore, it is necessary to control the quantities and distributions of brittle Ti-Fe intermetallics in the joint. The amount of melted base materials was controlled by changing laser offset to control the melted proportion and thus control the quantity and distribution of brittle Ti-Fe intermetallics in weld. When laser beam was on the SS side, melting amount of Ti alloy in weld was decreased. When laser beam was on the Ti alloy side, melting amount of SS in weld was decreased. When the laser offset was 0.35 mm away from SS side, the sample realizes the effective connection between Ti alloy and SS. A compound layer was formed at the SS side with the main microstructure of β-Ti and TiFe2. The joint fractured at the compound layer with the maximum tensile strength of 182 MPa. Microstructures and mechanical properties of joints were improved by changing laser offset.