Research On Microstructures And Mechanical Properties Of High Strength Casting Al-10.5Si-Zn-Mg Alloys

The middle plate is one of the three core components of smart phones,which supports and carries the core components of smart phones.It requires not only sufficient strength and stiffness but also complex structure.Compared with stainless steel or deformed aluminum alloy middle plates,the aluminum alloy middle plates produced by casting method have the advantages of simple process,high production efficiency and low cost,and have a good application prospect.However,the traditional casting aluminum alloys can not meet the requirement of 5G mobile phone middle plate performances,so it is necessary to develop new casting aluminum alloy materials.In this paper,the Al-10.5Si-Zn-Mg cast aluminum alloys were studied,and the effects of Mg contents and Zn contents on the microstructures and mechanical properties of the alloys were studied by means of mechanical property testing,metallographic microscope,scanning electron microscope,X-ray diffraction,etc..The effect of heat treatment on microstructures and mechanical properties of the alloys is also analyzed.The main conclusions are as follows:?1?With the increase of Mg contents,the area fraction of?-Al in Al-10.5Si-5Zn-xMg alloys gradually increases,the amount of bulk silicons increases,the size of them also increases.The iron-rich phases change from fine particles to needles and thick Chinese-like.The number of Mg₂Si phases gradually increases and their size also gradually increases.When the Mg content is 0.5%and above,Mg elements dissolve in the?iron phases to form the?-Al₈Mg₃?Fe,Mn?₆ phases.As the Mg contents increase,the tensile strength of the as-cast alloys tends to increase first and then tend to be stable,while the plasticity gradually decreases.When the Mg content is 0.5%,these alloys show the best mechanical properties with a strength of 265MPa and an elongation of 4.8%.?2?The strength of as-cast Al-10.5Si-xZn-0.5Mg alloys gradually increases with the increase of Zn contents,and their plasticity shows the opposite trend.When the Zn content is8.0%,the strength of the alloys reach the maximum value,and the tensile strength and yield strength are 272 MPa and 239 MP,respectively.And Zn elements are mainly uniformly distributed in the?-Al matrix in the form of solid solution,and no obvious zinc-rich compounds are found.?3?After T6 treatment,the silicon phases of Al-10.5Si-5Zn-xMg alloys significantly spheroidized.At the same time,the Mg₂Si phases dissolve and their area fraction decreases.Some coarse Chinese-like iron-rich phases are enriched with a large amount of fine silicon phases.However,the microstructures of the alloys did not change significantly after T1 heat treatment.?4?When Mg elements are not added to the Al-10.5Si-5Zn-xMg alloys,the strength of the alloys after heat treatment is lower than that of the as-cast alloys,and the strength of the T6state is higher than the T1 state.When Mg elements are added to the alloys,the strength of the alloys has been significantly improved compared with that of the as-cast state after heat treatment.And with the increase of Mg contents,it shows a trend of first increasing and then decreasing.However,the plasticity of the alloys after heat treatment is lower than that of the as-cast state,and gradually decreases with the increase of Mg contents.?5?After T6 treatment,the hardness of Al-10.5Si-xZn-0.5Mg alloys has two maximum values during the aging process,and the peak aging time of both times was advanced with the increase of Zn contents.When the alloys reach the peak aging,the hardness and strength of the alloys increase with the increase of Zn contents,and the plasticity changes in the opposite trend.