Effect Of Cold-Rolled And Annealing Treatment On Microstructure And Corrosion Resistance Of Mg-Li Alloys

Ultra-light Mg-Li alloy has many advantages,such as high specific strength and stiffness,great conductivity and excellent ability of room temperature deformation.It has an extraordinary market potential in aerospace,3C industry and high-tech industry,but its poor corrosion resistance greatly limits its application.In this paper,the as-cast alloys of Mg-5Li,Mg-9Li and Mg-9Li-1Zn?LZ91?were studied.The different cold-rolling reductions and corresponding annealing treatments were carried out for the three alloys respectively.The microstructure was observed by optical electron microscope?OM?and scanning electron microscope?SEM?;The phase composition was determined by X-ray diffractometry?XRD?and energy dispersive spectroscopy?EDS?.The corrosion resistance of alloys was investigated systematically by electrochemical measurements and immersion tests to explore the effects of different cold-rolling reductions and corresponding annealing treatment on the corrosion mechanism and corrosion resistance of test alloys.The main conclusions of this paper are summarized as follows:?1?The as-cast Mg-5Li alloy is composed of 94.8%?-Mg phase and 5.2%network-like?-Li phase.The as-cast Mg-9Li alloy consists of 34.2%massive?-Mg phase and 65.8%?-Li phase.The LZ91 alloy contains lath-like?-Mg phase disorderly distributed,?-Li phase,a little MgLi₂Zn and MgLiZn phases,wherein the?-Mg phase and?-Li phase are about 25.6%and 74.4%respectively.?2?The cold-rolled alloys of Mg-5Li,Mg-9Li and LZ91 are elongated along the rolling direction.The microstructures are further refined and elongated with the increase of cold-rolling reductions.The recrystallized grains were not observed in the cold-rolled and annealed Mg-9Li alloys.However,the obvious recrystallized grains were observed in the cold-rolled and annealed LZ91 alloy,which mainly appear at the phase boundary of?-Mg and?-Li phases leading to grain refinement.?3?The corrosion resistance of Mg-5Li,Mg-9Li and LZ91 alloys has a similar result in electrochemical measurements and immersion tests.The cold-rolling treatment has a significant effect to improve the corrosion resistance of alloys.The alloys show better corrosion resistance with the increase of cold-rolling reductions.After annealing,all alloys exhibit superior corrosion resistance comparing with the corresponding cold-rolled alloys.?4?Pitting firstly occurs in the?-Li phase with the lower electrode potential of LZ91 alloy.With the increase of immersion time,more pits appear at the phase boundary between?-Mg phase and?-Li phase which are expanded rapidly and joined together.In addition,the number of pits on the surface of?-Li phase is significantly more than that on the?-Mg phase,which proves that pitting mainly extends in the?-Li phase.