Mechanical Responses of Superlight β-Based Mg-Li-Al-Zn Wrought Alloys under Resonance

Abstract

To extend the application of lightweight Mg alloys in the automotive industry, this study suggests a b-based Mg-Li alloy (LAZ1110) with superior vibration fracture resistance by means of material design. In the coldrolled state, a strengthened b matrix by the additions of Al and Zn, as well as intergranular platelike a precipitates, which are able to stunt the crack growth, contributes to a comparable vibration life with commercial Mg-Al-Zn alloys under a similar strain condition.Due to the ultralow density and cold working ability, Mg-Li alloys, known as superlight alloys, have great potential for use as a structural material for transportation systems and portable electronic devices. An increase in the Li addition brings about the transformation of a (hcp) fi a + b (bcc) fi b and also an improvement of ductility along with the reduction in both the strength and strain hardening exponent. [1] To obtain a good combination of excellent formability and fair strength, Al, Zn, and Ag have been added for alloying modification. The literature indicates that the alloys containing Al and Zn are amenable to solution hardening and also aging hardening. [2] In the application of transportation systems, fracturing may occur in the structure under vibrating conditions, particularly when the vibration frequency meets local or general resonance even though magnesium is regarded as an excellent damping alloy. It has been reported that Mg alloys with high Li content possess great damping capacity but inferior strength, resulting in a poor vibration fracture resistance compared to Mg-AlZn when suffering the same vibration deformation. [3] The objective of this study is to develop a vibrationresistant superlight b-based Mg-Li alloy by way of alloying and process control. Nanoindentation was employed to examine the mechanical properties of each constitutional phase.The test materials include two Mg-Li alloys with the Li content, respectively, close to the left side and right side within the a + b two-phase region in which the Li content was from 5 to 11.5 wt pct. Those are Mg-11.2 wt pct Li-0.95 wt pct Al-0.43 wt pct Zn (LAZ1110) and Mg-5.71 wt pct Li-0.11Al wt pct-0.01 wt pct Zn (LA60) prepared for comparison. The compositions were analyzed by a glow discharge spectrometer. The as-received Mg-Li plates fabricated by extrusion were cold rolled to 3.3-mm sheets (rolling reduction: 35 pct) and then sectioned along the transverse direction. Parts of the cold-rolled LAZ1110 sheets were annealed at 250°C for 1.5 hours and referred to as the O samples. Phase identification of the samples was performed by an X-ray diffractometer operated at 30 kV and Cu K a radiation was used, with a scanning speed of 1 deg/min.In order to collect mechanical data for reference, tensile tests were performed. Rectangular specimens (gage length section: 20 mm 9 5 mm 9 3 mm) were prepared for tensile testing. The initial tensile strain rate was kept at 8 9 10 À4 s À1 . The mechanical performance of individual phase was evaluated by nanoindentation testing usin...

Orientation-dependent microstructure and shear flow behavior of extruded Mg–Li–Zn alloys

“…Some of the possible effective ways to improve formability of wrought Mg alloys are microstructural refinement [7,8], deformation at elevated temperatures [9,10], and use of alloying elements [11,12]. Among different elements, Li has the ability of decreasing density and introducing considerable ductility in the Mg alloys [2].…”