Compatibility Study Of Low Temperature Inorganic Phase Change Materials With Aluminum Alloy Packaging Materials

There are higher and higher demands on the heat dissipation of electronic systems,due to the size miniaturization of electronic devices and the high power of integrated circuits.The widespread attentions were attracted to apply inorganic phase change materials for the heat dissipation systems of integrated circuits,due to their non-combustibility and high thermal conductivity.The applications of inorganic phase change materials were limited in practical engineering because of their large subcooling,phase separation and compatibility with packing metals.In this paper,the The eutectic mixed compound（later called MNH-MCH composite phase change material）of magnesium nitrate hexahydrate and magnesium chloride hexahydrate with different ratios were prepared and their thermophysical properties were tested by DSC technique.At the same time,the subcooling degree of the phase change material was decreased by the addition of the nucleating agent.Based on the above,The compatibility of the MNH-MCH composite phase change material with 6063,3A21,ZL104 aluminum alloys and 3D-printed 3A21 aluminum alloy were studied.The following conclusions were obtained:（1）The effects of differently added MNH volumes on the phase change enthalpy of magnesium-based composite phase change materials were investigated and their thermophysical properties were tested by DSC technique.The results showed that there were a endothermic peak and exothermic peak when the volume of MNH was controlled from 30-60%,indicating that the mixed compound of MNH and MCH formed eutectic mixture.The highest phase change enthalpy was up to 155.46 J/g when MNH was added at57 wt.%,phase change temperature was 58.5℃,and the subcooling degree was 11.7℃.The effects of nucleating agents Ca SO₄·2H₂O,Mg Br₂·6H₂O and Sr Cl₂·6H₂O on the subcooling degree of MNH-MCH composite phase change material were studied.It was found that Sr Cl₂-6H₂O was effective in reducing the subcooling degree of MNH-MCH composite phase change material,and the subcooling degree was reduced to 0.4℃when Sr Cl₂·6H₂O was added by 0.3%.and the subcooling degree kept unchanged even after 50cycles of solid/liquid transition.（2）The corrosion behaviors of 6063 and 3A21 aluminum alloys in the solid-liquid transition process of MNH-MCH composite phase change material were studied by weight loss.The results showed that the corrosion rate of 6063 aluminum alloy firstly increased with time,and then decreased.Finally,it tended to be stabilize;while the corrosion rate of3A21 aluminum alloy showed gradually decreasing trend with time.The corrosion morphology of these two kinds of aluminum alloys showed local corrosion characteristics,and the corrosion products contained O,Cl and Al,which was induced by the acidic corrosion medium containing Cl^-.（3）EIS of 6063 and 3A21 aluminum alloy at the early stage of immersed in the molten liquid of MNH-MCH composite phase change material showed the two time constants.With time elapsed,the inductive loop was observed in a low frequency region,showing local corrosion occurred in the acidic corrosive environment containing Cl^-.Compared to that in molten phase change material,the EIS of these two kinds of aluminum alloys in solid status during solid-liquid transition of MNH-MCH composite phase change material showed a single time constant;While in molten status,their EIS was composed of two capacitive loops with two time constants.The inductive loop in a low frequency domain was not found.The solution resistance（Rs）in the solid status was about ten times higher than that in liquid status,due to the large resistance to ion migration in the solid status compared to that in the liquid status.（4）The corrosion behavior of cast and 3D printed aluminum alloys in the phase change material were further studied.The results showed that the corrosion behaviors of cast and 3D printed aluminum alloys in solid-liquid transition were basically the same.However,the corrosion rate of 3D printed aluminum alloy was higher compared with that of cast aluminum alloy when they immersed for a long time.Although the corrosion morphologies of the aluminum alloys manufactured by different forming processes showed pitting with the same corrosion product components.In addition,there are obvious differences between the electrochemical behaviors of the aluminum alloys manufactured by different forming processes in molten liquid of composite phase change material.Although the impedance spectra of the aluminum alloys manufactured by different forming processes showed two time constants,the capacitive loop was observed in a low frequency domain for cast ZL104,while the inductive loop was found in a low frequency domain for the 3D printed aluminum alloy.During solid-liquid transition,EIS of the aluminum alloys manufactured by different forming processes had two time constants,but ZL104 has a relatively higher impedance.