Erosion Behavior Of Phase Change Energy Storage Al Alloy Melts Against 304 Stainless Steel Surface

The successful application of phase change energy storage technology is related to not only thermal properties of energy storage materials,but also the compatibility between energy storage material melts and container materials.Studies have shown that: phase change energy storage Al alloys have excellent thermal properties,and have a promising application prospect in solar thermal power generation and other high temperature storage fields.But it restricts their further development and application that the erosion of high temperature Al alloy liquids against iron based materials is serious.In this paper,erosion experiments were designed to solve these problems.Eight kinds of energy storage alloy that were Al-12Si-xCu alloy,Al-xSi-10 Cu alloy and Al-12Si-15Cu-2Mg alloy were chosen as the energy storage materials.And the 304 stainless steel was selected as the container material.The erosion behavior of Al alloy melts against 304 stainless steel surface was studied under the condition of the different temperature,time and elements(Cu,Si and Mg).Combined with XRD analysis,metallographic analysis and EDS analysis and other instruments,the erosion mechanism of phase change energy storage Al alloy melts against the 304 stainless steel material was revealed.These studies can provide experiments and theoretical basis for reducing the erosion ability of phase changes storage energy Al alloy melts.For eight kinds of alloy studied in this paper,when the erosion time is 24 h and the erosion temperature range is 580℃~660℃,the erosion rate and erosion thickness of 304 stainless steel increase with the temperature increasing.And when the temperature exceeds 640℃,erosion rate and erosion thickness will increase significantly.As a result,the influence of temperature on the erosion behavior is remarkable.The erosion ability of Al alloy melts is week at low temperature.For eight kinds of energy storage alloy studied in this paper,when the erosion temperature is 620℃ and the erosion time increases from 24 h to 120 h,the erosion rate decreases with the increase of time,and it will reach the dynamic equilibrium state when reducing to a certain value.In the process of Al-xSi-10Cu(0≤x≤15)alloy melt eroding the 304 stainless steel,with the content of Cu increasing,the erosion rate and erosion thickness decrease.In the process of Al-xSi-10Cu(6≤x≤15)alloy melt eroding the 304 stainless steel,when the content of Si increases from 6wt.% to 9wt.%,the erosion rate and erosion thickness decrease firstly.When the content of Si increases from 9wt.% to 12 wt.%,the erosion rate and thickness increase slightly.And while the content of Si is 12 wt.%~15wt.%,the erosion rate and thickness increase significantly.The addition of 2wt.% Mg element in Al-12Si-15 Cu alloy melt can reduce the erosion rate and erosion thickness.According to experiment results and the dynamics analysis,the erosion type of Al-xSi-yCu-zMg alloy melt against the 304 stainless steel is diffusion erosion,the erosion is mainly due to the diffusion of Al element,and Cu element and Mg element do not participate in the erosion reaction.The erosion layers are divided into two regions which are the inner layer contacting the 304 stainless steel and the outer layer contacting the Al alloy melt.The inner erosion layer is mainly composed of Al95Fe4 Cr phase,banded and denser.And its microhardness is bigger than the outer layer’s.For the composition of the outer erosion layer,when the Si element content is low and the erosion time is short,it is mainly composed of Fe2Al5 phase.At this time,Si can prevent the diffusion of elements by filling the vacancy of Fe2Al5 phase.When the Si element content is high and erosion time is long,the outer erosion layer is mainly composed of FexSiyAlz phase,FeAl phase and Al13Fe4 phase.While the FexSiyAlz phase growth rate is low,and can prevent the diffusion of elements.As a result,the erosion rate is reduced.For the outer erosion layer contacting the Al alloy melt,it can become loose and even crack because of vacancy defect aggregation during the process of erosion.Al alloy liquid go into these pores,and make the local erosion layer off.The peeling pieces in the liquid alloy are stretched to rupture,becoming finer pieces,and ultimately completely melted.The Cr element exists in the form of Al95Fe4 Cr intermetallic compound,which can hinder the diffusion of elements.