Investigating the weld joint characteristics of AZ31 and AZ91 magnesium alloys produced by friction stir welding

In this work, FSW was used to join AZ31 and AZ91 magnesium (Mg) alloys to investigate the mechanism behind joint formation and its mechanical performance. The cross-sectional microstructure of the weld zone clearly indicated a strong metallurgical bonding between AZ31 and AZ91 sheets in addition to the mechanical interlocking due to the mixing of both base materials. Uniform hardness (62.9 +/- 4.5 HV) was recorded in the weld joint and the values were between AZ31 (59.8 +/- 2.4 HV) and AZ91 (78.7 +/- 19.5 HV). Tensile test results demonstrated decreased strength (145 +/- 4.2 MPa) compared with the base alloys (265 +/- 7.3 MPa and 190 +/- 4.8 MPa for AZ31 and AZ91, respectively. Ductility was noticed as decreased as reflected by the lower % of elongation for the weld joint compared with both AZ31 and AZ91 base materials. The fractography studies of the samples suggest a brittle mode of fracture in the weld joint similar to that of AZ91 base material. Dans ce travail, on a utilis & eacute; FSW pour assembler les alliages de magn & eacute;sium (Mg) AZ31 et AZ91 dans le but d'& eacute;tudier le m & eacute;canisme & agrave; l'origine de la formation du joint et ses performances m & eacute;caniques. La microstructure de la section transversale de la zone de soudure a clairement indiqu & eacute; une liaison m & eacute;tallurgique forte entre les t & ocirc;les de AZ31 et AZ91 en plus de l'enclenchement m & eacute;canique en raison du m & eacute;lange des deux mat & eacute;riaux de base. Les compos & eacute;s interm & eacute;talliques & eacute;taient consid & eacute;rablement r & eacute;duits dans la zone du noyau ainsi que l'effet d'affinement des grains. On a enregistr & eacute; une duret & eacute; relativement uniforme (62.9 +/- 4.5 HV) dans le joint de soudure et les valeurs se situaient entre AZ31 (59.8 +/- 2.4 HV) et AZ91 (78.7 +/- 19.5 HV). Les r & eacute;sultats d'essai de traction ont pr & eacute;sent & eacute; une r & eacute;sistance r & eacute;duite (145 +/- 4.2 MPa) par rapport aux alliages de base (265 +/- 7.3 MPa et 190 +/- 4.8 MPa pour AZ31 et AZ91, respectivement). On a not & eacute; que la ductilit & eacute; avait diminu & eacute;, comme le refl & egrave;te le pourcentage d'& eacute;longation plus faible du joint soud & eacute; par rapport aux mat & eacute;riaux de base, AZ31 et AZ91. Les & eacute;tudes fractographiques des & eacute;chantillons sugg & egrave;rent un mode de rupture fragile dans le joint de soudure similaire & agrave; celui du mat & eacute;riau de base AZ91.