Study On The Si-P Series And Cu-P Series Phosphorus-Rich Alloys

Phosphorus-rich alloys such as Si-P and Cu-P series alloys were systematically studied using high scope video microscope (HSVM), electron probe micro-analyzer (EPMA), X-ray diffractometer (XRD) and field-emission scanning electron microscope (FESEM). The refinement and modification effects of Si-P series alloys on hypereutectic Al-Si and Al-Mg-Si were investigated and a proper refining process was established. Also, the phase compositions and microstructures of multicomponent phosphorus-rich alloys like Si-Mn-P, Si-Zr-Mn-P and Si-Cr-Mn-P were studied. In addition, the effect of transition metal elements on the phosphide species, microstructures and properties of Cu-P were analyzed. The major research results in the present study are as follows:(1) The refinement and modification effects of Si-P series alloys on the primary Si and Mg2SiIt is found that when the Si-P series alloys are directly added into the Al-24Si alloy melt, the refinement effects are not achieved because the Si-P series alloys are difficult to dissolve at normal melting temperature. But when the Si-P series alloys are added into Al melt before the addition of Si, the best refinement effect can be achieved. The refinement mechanism can be described as:AlP particles form easily while Si-P series alloys could dissolve quickly into Al melt. Some of them can act as the nuclei of primary Si during the solidifying process, and thus the primary Si is refined. Microstructures of Si-P series alloys have great influences on their solution rate and refinement effect. It is found that Si-P with more eutectic structures has better refinement efficiency. Microstructure of Si-P alloy is refined greatly by rapid solidification processing. AlP particles disperse more uniformly in the alloy made by adding the rapidly-solidified Si-P to Al, which have better refinement effect on Al-24Si alloy.The Orthogonal Experiment results show that the influence of refinement parameters of Si-P on the size of primary Si decreases in the following order: refinement temperature> addition level> holding time. The optimized refinement parameters are:refinement temperature of 810℃, addition level of 0.35%, holding for 30min+50min (Si-P is added firstly to the Al melt, Si is added 30min later, then holding another 50min).The high-efficiency Si-P series alloys with high phosphorus content have good refinement effects on primary Mg2Si in Mg-Si and Al-Mg-Si alloys. The phosphorus distributes uniformly in Mg2Si particles of Mg-Si-Mn-P alloy which could be used to refine primary Si in hypereutectic Al-Si as well as primary Mg2Si in hypereutectic Mg-Si.(2) The Preparation of Si-TM-P alloys and their refinement and strengthening effect on Al-Si piston alloysIt is found that there is no ternary compound when the composition of Si-Mn-P alloy lies in the MnSi1.75-x-Si-MnP region. Microstructural formation rule of this typical Si-Mn-P alloy is described as follows:the primary Si or MnP phases are firstly surrounded by (Si+MnP) binary eutectic structure with variety of morphologies and then by ternary eutectic (Si+MnSi1.75-x+MnP) with binary morphology due to divorced eutectic depended on the particularity of certain Si-Mn-P alloys. According to the formation rule of microstructures, Si-40Mn-15P with more eutectic structures is prepared. Si-40Mn-15P can be easily dissolved at the common melting temperature of Al-24Si. Besides that, the primary Si is refined as well as heat-resistant Fe phase can be found when Si-40Mn-15P is used to refine A390 piston alloys.Phosphorus-rich phases in prepared Si-Zr-Mn-P alloys are existed as ZrP which show dendritic morphology and distribute uniformly. The refinement effect on primary Si is good and eutectic Si becomes short due to effect of Zr on eutectic cell during treating A390 alloys. Besides that, heat-resistant Fe phase can also be found. Phosphorus-rich phases in prepared Si-Cr-Mn-P alloys contain Mn, Cr and Si elements. The refinement effect on primary Si is also good when treating A390 alloys. What's more, the amount of heat-resistant Fe phase locating around the eutectic increases and the morphology becomes more regular.(3) Effect of transition metal elements on the phosphide species, microstructures and properties of Cu-PThere would be transition phosphides such as TiP, Cr12P7 and ZrP in Cu-P alloy after introducing Ti, Cr and Zr respectively into Cu-14P alloys with single CU3P phase. Microhardness value of TiP is higher than ZrP and Cr12P7. The microhardness values of Cu alloys can be increased greatly due to these phosphides.Effects of Ni on the microstructures and properties of Cu-8P have been explored. It is found that the eutectic structures show obvious changes with different Ni addition. The Cu3P phases change from lamellar structures to coarse dendrites firstly, and then to fine vermicular structures. The eutectic structures become denser with increasing Ni addition amount. It is also interestingly found that Cu-P alloys with addition of 3% Ni possess the lowest hardness value which is caused by the combined effect of eutectic deviation and weak solid solution strengthening due to the addition of Ni. In addition, Cu-8P with 3%Ni addition has the least corrosion proneness owing to the formation of new phase.