Effect Of Heat Treatment And Deformation On Microstructure And Internal Friction Of AZ31 And Mg-9Gd-3Y Magnesium Alloys

In this paper,as-rolled AZ31 magnesium alloy and as-cast Mg-9Gd-3Y alloy were chosen to be the research object.Optical microscope?OM?,scanning electron microscope?SEM?,transmission electron microscope?TEM?were applied to observe the microstructures.The pre-deformations and mechanical properties were tested on versatile testing machine.Internal friction-temperature spectrum were investigated by MFP-1000 multifunctional internal friction apparatus.Discussion and analysis the effects of heat treatment and pre-deformations on the microstructure,mechanical properties and internal friction.The following main research results were obtained:?1?The results revealed that the rolled sample underwent recrystallization after an aging treatment at 623 K.The average grain diameter of the sample aged for 0.5 h was 8.5?m and the average grain size increased gradually with increasing aging time.This sample was used for tensile deformation tests.The results revealed that the density of dislocations and twin crystals increased with increasing deformation.An intragranular cellular substructure formed at a deformation level of 5%,and the deformation cells were further refined when the deformation was increased to 15%.Two internal friction peaks were observed for each of the rolled samples,aged at 623K samples,and deformed samples.P1 was around 450 K,corresponding to an activation energy of 116¹20 kJ/mol,which was attributed to grain boundary sliding.P2 was around 525 K,corresponding to an activation energy of 132¹39 kJ/mol,which was attributed to internal friction correlated with precipitation of a second phase.?2?The as-cast microstructure of the Mg-9Gd-3Y experimental magnesium alloy is mainly composed of a white matrix and gray dendrites distributed along the grain boundary in a skeleton or dendritic shape.The alloy is mainly consist of of?-Mg,Mg₅?Gd,Y?and Mg₂₄?Gd,Y?₅ phases.This as-cast sample was used for tensile deformation tests,the results revealed that the density of dislocations increased with increasing deformation.When the deformation is 10%,dislocation entanglement inside the grain forms cellular substructure,and twin crystals appear at the same time.Two internal friction peaks were observed for as-cast and deformed samples.The P1 peak appears at about 540K,its activation energy is between 135 kJ/mol and 140kJ/mol,which is the grain boundary slip peak;the P2 peak is around 620 K,and its activation energy is between 155 kJ/mol and 160 kJ/mol,which was attributed to internal friction correlated with precipitation of a second phase.?3?The results show that,the second phase dissolved into the matrix after the homogenization heat-treatment at 500?,with the increase of the holding time,the grain size did not change much,more cuboid-shaped particles are founded and distributes in the and boundary.The yield strength and tensile strength decrease with the increase of solid solution time,and the elongation increases first and then decreases.After the as-cast condition is treated at 200?,the rare earth phase with cuboid-shaped particles and gray bright color distributes along the grain boundary,and the gray bright rare earth is distributes with the increase of the holding time,and there is no evident grain growth,the yield strength and tensile strength first increase and then decrease.?4?There are two temperature internal friction peaks in the heat-treatment sample.The P1 peak is the grain boundary slip peak,and the P2 peak is the internal friction peak related to the second phase precipitation;In the sample of heat-treatment at500?,with the prolongation of the holding time,the peak height of P1 become higher,the peak temperature did not change much,and the peak height and peak temperature of P2 become lower.In the treated sample at 200?,the peak heights of P1 and P2 become higher with the increase of holding time,the P1 peak temperature shifts to the right,and P2 peak temperature shifts to the left.