Digital Image Correlation Used for Experimental Investigations of Al/Mg Compounds

Abstract

Al/Mg compounds produced by hydrostatic extrusion exhibit unique characteristics in terms of high strength and low weight, which are required in lightweight safety parts. The compound interface between the core and sleeve is a brittle intermetallic phase consisting of Al 2 Mg 3 and Al 12 Mg 17 . However, a certain plastic deformability is required for subsequent processing of the semi-finished product by forming. To obtain a basic understanding of the deformation behaviour of the interface, the Digital Image Correlation is used together with a new analysis procedure based on the approximation of the displacement field with polynomial functions. The procedure is first tested with a bending test. The specimens exhibit a remarkable deformation behaviour under bending at high temperatures, which is confirmed by the results of radial upsetting tests. Even under a multi-axle load, the interface maintains a full material joint, though fragmentation occurs, and a new secondary interface between the fragments can be observed. In addition, an evaluation of light microscopy images and Eulerian Hencky strain values at the interface, which are based on the Digital Image Correlation results, imply a connection between the strain and the boundary layer's appearance.

Experimental and Numerical Investigation of AA5052-H32 Al Alloy with U-Profile in Cold Roll Forming

“…For the gauge length based computation, standard tensile test procedures were used as follows: where as , , and are the engineering stress, the engineering strain, the true stress, and the true strain, respectively [ 24 , 25 , 26 , 27 , 28 , 29 , 30 , 31 , 32 , 37 ]. In Equation ( 1 ), F , , , are the load applied, the initial area of sample cross-section, the length change and the gauge length, respectively.…”

“…Considering the volume constancy, the longitudinal (length change) and transverse (width change) strains were computed from the tensile sample after roughly 20% plastic strain because the standard procedures generally suggest that the best range to determine the R –value is after the material yield point and before the tensile strength. The plastic strain ratio ( R ) can be determined as shown in Equation ( 3 ) [ 24 , 25 , 26 , 27 , 28 , 29 , 30 , 31 , 32 ]: …”

“…Compared to conventional measurement systems such as tensile test equipped with the mechanical extensometer, strain measurement probes, and 3D coordinates estimation instruments, the DIC technique is extensively employed to measure the large deformation and strains because of its ease of convenience during the forming experiments. However, the sample’s surface must be prepared with a proper random speckle pattern to achieve more accurate results; otherwise, it might lead to wrong material data estimation [ 24 , 25 , 26 , 27 , 28 , 29 , 30 , 31 , 32 ]. The authors, wang et al [ 32 ], Minsso Kim et al [ 33 ], Kupke et al [ 34 ], and Szabolcs Szalai et al [ 35 ], have successfully implemented the DIC method for the tensile test to estimate the material properties.…”

Process Chain for the Production of a Bimetal Component from Mg with a Complete Al Cladding

“…Figure 1a,b shows a cross-sectional schematic view of the pressing billets with a Mg core and an Al cladding. The fracture and mechanical properties of the material composites have been investigated in detail by Lehmann [13,14] and Kirbach [15,16]. They found that the interface tensile strength at room temperature was 125 to 145 MPa, and the formability increased at elevated temperatures.…”

A Fragmentation Criterion for the Interface of a Hydrostatic Extruded Al-Mg-Compound

“…Furthermore, a good formability of the compound at high temperatures could be shown, which resulted partly in failure through large plastic deformation under bending. In these cases, the bending strength of the boundary layer is higher than the yield stress of the basic materials, which is important for further forging processes [21].…”