Research On Microstructure And Performances Of AZ91-RE-xCu Alloys

In this paper,taking AZ91-RE-xCu(x=0,1,2,3,4 wt%)alloy as the research object,a series of AZ91-RE alloys with different copper contents were prepared by hot extrusion and heat treatment.The microstructure evolution of AZ91-RE-xCu alloy in as-cast,extruded,and heat-treated states was studied by OM,SEM,and EDS.The electronic universal testing machine was used to study the mechanical properties of AZ91-RE-xCu alloy in as-cast,extruded and heat-treated states.The corrosion behavior of AZ91-RE-xCu alloy in the as-cast,extruded and heat-treated state was studied by hydrogen evolution immersion experiment,weight loss experiment and electrochemical test,and the factors affecting the corrosion behavior of the alloy were discussed.The results are as follows:(1)In the as-cast AZ91-RE-xCu(x=0,1,2,3,4 wt%)alloy,the microstructure of the AZ91-RE alloy without Cu element is composed of?-Mg and distributed along the grain boundary.Due to the decomposition of the?-Mg₁₇Al₁₂phase,a new T-Al Cu Mg Zn phase appears in the alloy with the addition of Cu element.In addition,the addition of Cu element refines the crystal grains to a certain extent,and the fracture strength(?_f)of the as-cast AZ91-RE-xCu alloy is increased from 216MPa(AZ91-RE)to 297MPa(AZ91-RE-4Cu),an increase of 37.5%.The corrosion rate increases with the increase of Cu content.The corrosion rate of AZ91-RE-4Cu alloy is the largest,and the compressive strength is also the largest.(2)In the extruded AZ91-RE-xCu(x=0,1,2,3,4 wt%)alloy,the microstructure of the extruded Cu-free AZ91-RE alloy is composed of dynamically recrystallized grains?-Mg and?-Mg₁₇Al₁₂,and the Cu-containing alloy microstructure is mainly composed of?-Mg and the new T-Al Mg Zn Cu phase.When the Cu content is less than 3%,the grains are refined to a certain extent.When the Cu content is increased to 4%,the grain size is slightly coarsened to 8.9?m,and the extruded AZ91-RE-3Cu alloy has the largest Breaking strength(405MPa),which is due to the combined effect of grain refinement strengthening and second phase strengthening.In addition,the extruded AZ91-RE-3Cu alloy also takes into account a relatively fast corrosion rate,so it is expected to become an ideal material for new petroleum fracturing balls.(3)In the heat-treated AZ91-RE-xCu(x=0,1,2,3,4 wt%)alloy,the precipitation of point-like second phases is significantly increased,and a large number of precipitates are dispersed and distributed inside the grains,and with As the Cu content increases,the precipitates after heat treatment also increase.At the same time,as the Cu content increases,the average grain size of the heat-treated alloy decreases,but the grain size of the as-cast alloy increases significantly.Therefore,the heat-treated alloy has the smallest compressive strength.In addition,the heat-treated AZ91-RE-xCu alloy has the fastest corrosion rate among as-cast and extruded alloys of the same composition,and with the increase of Cu content,the corrosion rate of the heat-treated AZ91-RE-4Cu alloy reaches the fastest.But the compression resistance is low.