Analysis And Control Of Pinhole Defects In A356 Aluminum Alloy Cylinder Head Castings

As the most commonly used casting material in the non-ferrous casting industry,A356 aluminum alloy is widely used in various fields such as automotive,marine and aerospace.However,the problem of pinhole defects caused by the high hydrogen content of the aluminum liquid has become the biggest problem in the foundry industry.As the most important part of the automobile engine,the automobile cylinder head needs to withstand high impact load and thermal load,and the occurrence of pinholes will degrade the mechanical performance of the cylinder head,which seriously jeopardizes the reliability of the cylinder head.There are many problems causing pinholes in castings,including inclusions,cooling rate,deterioration,etc.,all of which are closely related to hydrogen in the aluminum liquid.In this paper,the pinhole defect of A3 56 aluminum alloy cylinder head is analyzed and the pinhole defect is controlled for actual production.The analysis of the pinhole defect of the cylinder head and the formation of the cause and the influence of the refining parameters on the refining effect and the rest process are carried out.Study on the effect of hydrogen content in aluminum liquid.Experimental results show:The analysis and formation of the pinhole defect of the cylinder head;the pinhole type of the cylinder head is the precipitation type pinhole,which causes the pinhole to be generated because the hydrogen content in the aluminum liquid is high.By analyzing the position around the pinhole defect,it is found that the surrounding tissue of the pinhole defect is accompanied by roughening.The analysis of the internal components of the pinhole revealed that the C and O inclusion elements in the pinhole were higher.The effect of refining parameters on the refining effect;the graphite rotor Polarq?200×80 liquid surface disturbance value is lower than the graphite rotor SPR??220 × 85;the graphite rotor Polar?200× 80 degassing rate is higher than the graphite rotor SPR?220 × 85;When the refining temperature is 730 ? and the rotation speed is 300 r · min-1 nitrogen flow is 30 schf and the refining time is 12 min,the refining effect is the best and most suitable for practical production.The effect of the static process on the hydrogen content of the aluminum liquid;the higher the ambient humidity,the higher the hydrogen content of the aluminum alloy;the addition of Sr element in the aluminum liquid can cause the hydrogen absorption phenomenon of the aluminum liquid to be aggravated.Among them,when the humidity is 75%RH,casting at 710 ?,and using cold iron to shorten the solidification time can effectively reduce the occurrence of pinhole defects.In actual production,Sr is used for metamorphism,and when the content is 64 ppm,the deterioration effect is the best.