Phase Evolution and Mechanical Behavior of the Semi-Solid SIMA Processed 7075 Aluminum Alloy

Two rolled plates of 7075 aluminum alloy were used as starting material. The plates were welded using a simultaneous double-sided friction stir welding (FSW) process. One way of obtaining feedstock materials for Semi-solid processing or thixoforming is via deformation routes followed by partial melting in the semi-solid state. As both the base plate materials and the friction weld area have undergone extensive deformation specimens were subjected to a post welding heat-treatment in the semi-solid range at a temperature of 628 • C, for 3 min in order to observe the induced microstructural changes. A comparison between the microstructural evolution and mechanical properties of friction stir welded plates was performed before and after the heat-treatment in the Base Metal (BM), the Heat Affected Zone (HAZ), the Thermomechanically Affected Zone (TMAZ) and the Nugget Zone (NZ) using optical microscopy, Scanning Electron microscopy (SEM) and Vickers hardness tests. The results revealed that an extremely fine-grained structure, obtained in the NZ after FSW, resulted in a rise of hardness from the BM to the NZ. Furthermore, post welding heat-treatment in the semi-solid state gave rise to a consistent morphology throughout the material which was similar to microstructures obtained by the thixoforming process. Moreover, a drop of hardness was observed after heat treatment in all regions as compared to that in the welded microstructure.

Section: Methodsmentioning

confidence: 99%

A Microstructural Evaluation of Friction Stir Welded 7075 Aluminum Rolled Plate Heat Treated to the Semi-Solid State

Chegeni

Kapranos

2018

“…The precipitates are identified as AlCuMg by EDS with a size of~1-5 µm, which agrees well with the result of OM in Figure 3. It is well known that when the Zn:Mg ratios are between 1:2 and 1:3 in the 7075 aluminum alloys, MgZn 2 precipitates are produced at aging temperatures below 200 • C and are the main strengthening factor in 7075 alloys [19], so further experiments are needed to prove the existence of MgZn 2 .…”

Section: Resultsmentioning

confidence: 99%

Effect of a Minor Sr Modifier on the Microstructures and Mechanical Properties of 7075 T6 Al Alloys

Sun

Wang

et al. 2017

Abstract:The influence of a minor strontium (Sr) modifier on the microstructures and mechanical properties of 7075 Al alloys was investigated in this paper. The grain size of cast 7075 Al alloys was refined from 157 µm to 115 µm, 108 µm, and 105 µm after adding 0.05 wt. %, 0.1 wt. %, and 0.2 wt. % Sr, respectively. The extruded 7075 Al alloys was refined with different degrees of Sr modifier. The mechanical properties were optimum when adding 0.1 wt. % Sr. The ultimate tensile strength (σ b ) increased from 573 to 598 MPa and the elongation-to-failure (δ f ) was raised from 19.5% to 24.9%. The microhardness increased from 182 to 195 Hv. The tensile fracture surface via scanning electron microscopy (SEM) revealed a transition from brittle fracture to ductile fracture as Sr increased from 0 wt. % to 0.2 wt. %. The result in this paper proved that the modifier can improve the properties of 7075 Al alloy.

“…First, by segregation of the alloying elements inside the solid grains, leading to the formation of fine liquid droplets during the partial re-melting, and, secondly, when grains are combined to reduce the solid-liquid interfacial energy during the heating stage of the thixoforming process, giving rise to the creation of relatively large liquid droplets contained within the sub-grains. Hence, the base metal consists of alpha-Al, eutectic liquid phase and occasional trapped liquid pools within sub-grains [5]. Figure 4 illustrates the micrographs of the EB welded plates.…”

Section: Microstructure Of the Base Materialsmentioning

confidence: 99%

“…Promising fabrication techniques are required to produce high quality and integrity parts for such applications. Hence, semisolid metal processing as a single step manufacturing method providing good quality near net shape products has been widely employed to aluminium alloys due to the advantages that this technology offers over the conventional casting techniques [5][6][7][8].…”

Section: Introductionmentioning

confidence: 99%

An Experimental Evaluation of Electron Beam Welded Thixoformed 7075 Aluminum Alloy Plate Material

Chegeni

Kapranos

2017

Two plates of thixoformed 7075 aluminum alloy were joined using Electron Beam Welding (EBW). A post-welding-heat treatment (PWHT) was performed within the semi-solid temperature range of this alloy at three temperatures, 610, 617 and 628 • C, for 3 min. The microstructural evolution and mechanical properties of EB welded plates, as well as the heat-treated specimens, were investigated in the Base Metal (BM), Heat Affected Zone (HAZ), and Fusion Zone (FZ), using optical microscopy, Scanning Electron Microscopy (SEM), EDX (Energy Dispersive X-ray Analysis), and Vickers hardness test. Results indicated that after EBW, the grain size substantially decreased from 67 µm in both BM and HAZ to 7 µm in the FZ, and a hardness increment was observed in the FZ as compared to the BM and HAZ. Furthermore, the PWHT led to grain coarsening throughout the material, along with a further increase in hardness in the FZ.