Effect of Intermetallic Compound Layer on Tensile Strength of Dissimilar Friction-Stir Weld of a High Strength Mg Alloy and Al Alloy

Abstract

The friction stir weldability of a fine-grained high strength AZ31B magnesium alloy to A5083 Al alloy was evaluated at various welding conditions, by using a tool with shoulder diameter of 15 mm, pin diameter of 5 mm and pin length of 3.9 mm. A square butt dissimilar joint without any defect was obtained at the condition of welding speed 100 mm/min, tool rotating speed 500 rpm and offset 0 mm. Higher or lower welding speeds or rotating speeds led to either the formation of defect or lack of bonding in the joint. Defects occurred also in the case that the offset was not 0 mm, i.e. the insertion position of the probe was on either Mg side or Al side, when tool rotating speed was 500 rpm and welding speed was 100 mm/min. The maximum tensile strength of the dissimilar joints in the present study was about 115 MPa, lower than that of Al alloy base metal (about 308 MPa). Transmission electron microscopy showed that an intermetallic compound (IMC) layer, which consisted of Al 12 Mg 17 and Al 3 Mg 2 , formed at the bonding interface of the joints, and it was found that the formation and growth of the IMC were controlled by the react diffusion of Mg and Al atoms, instead of the eutectic reaction. The present study demonstrated that the tensile strength of the dissimilar joints was mainly affected by the thickness of IMC layer and the mechanical interlock between magnesium and aluminum alloys. The tensile strength decreased remarkably with the increase in the thickness of IMC layer, which made the mechanical interlock weaker.

Effect of annealing on the interface microstructure and mechanical properties of a STS–Al–Mg 3-ply clad sheet

“…While the yield stress and ultimate tensile strength of A3 sample are just slightly smaller than the ones of A1, elongations up to initial and overall fractures are strongly decreased to 0.150 and 0.215, respectively, with the increase of annealing time from 1 to 3 h at 300 1C. This is meeting the expectations as the profound growth of the brittle intermetallic compounds by over-annealing do harmful effect upon the mechanical interlock at the interface [30,31]. However, this does not directly mean that there is not a variety of possibilities for improving mechanical properties of clad metals given by post-annealing which somewhat induces the generation of IMCs at interface.…”

Interface-correlated deformation behavior of a stainless steel-Al–Mg 3-ply composite

“…Taking the values of YS and UTS calculated on the basis of ROM into consideration, the results provide strong evidence that experimentally measured tensile strengths for the 3-ply sheet fabricated by roll bonding adopted in this study are obviously improved, regardless of annealing treatment, which is primarily attributed to the adequate interfacial strengthening. However, it was also found that the difference between the experimentally determined and ROM-based tensile strength decreased upon increasing annealing time, which implies that the profound growth of the brittle IMCs at interfaces by overannealing have a detrimental effect on the mechanical interlocking at the interface [24,25]. Unlike tensile strength, an estimate of homogeneous composite strain cannot be supported by means of ROM theory [26].…”

Beneficial Interface Geometry for Laser Joining of NiTi to Stainless Steel Wires

“…One proposed method is to use friction stir welding. This process reaches lower temperatures, and thus may help minimize intermetallic formation [6]. Friction stir welding of magnesium and aluminum has been shown to be possible, but it was found that the hardness across the joint became twice that of the base materials [7].…”