Effect of Zn on interfacial microstructure and properties of steel/aluminum dissimilar metal friction stir welded joints

Abstract

Zn powder with a thickness of 0.4 mm was sprayed on the steel side by ion spraying method The lap welding was carried out on the 3 mm thickness 6005A-T6 aluminum alloy and 3 mm thickness S420MC steel plate using FSW (friction stir welding). The effects of Zn on the interface morphology, microstructure, mechanical properties and interfacial growth of weld were studied by means of (XRD) and microhardness of (OM), scanning electron microscope (SEM), X-ray diffractometer and microhardness. The results show that both the steel/aluminum joint without Zn layer and the steel/aluminum joint with Zn layer form the special "flying edge" of friction stir welding at the interface and extending into aluminum matrix to form the joint of mechanical occlusion,AlFe,AlFe3,Al13Fe4 intermetallic compounds are produced at the interface. Steel particles are dispersed in aluminum matrix of steel/aluminum joint without Zn layer. The maximum tensile and shear load of the joint increase from 4826 N to 5628 N at the interface. The non-Zn layer steel/aluminum fracture joint is a typical "tough-brittle" hybrid fracture, and the Zn layer steel/aluminum joint is brittle fracture. The maximum microhardness value reduces from 388HV without Zn layer joint to 210HV with Zn layer joint.

Keywords

• low carbon steel
• aluminum alloy
• interface
• microstructure
• property
• intermetallic com-pound