Squeeze Casting 1-This technique which was invented in 1960, can be used for monolithic alloys as well as Discontinuously and Continuously reinforced MMCs. 2- There are two main differences between Squeeze casting and conventional pressure die casting: In Squeeze casting the applied pressure is within the range of 55-200 MPa , while in pressure die casting the maximum applied pressure is 17 MPa. In Squeeze casting the pressure is applied until the end of solidification, while in the other technique the pressure is used just for filling the mould.

The Advantages of Squeeze casting for monolithic alloys 1- Minimum gas porosity and shrinkage porosity due to applied pressure 2- production of near net shaped components (±0.05 mm tolerance), requiring minimum machining. 3- Increased production rate and ability for automation. 4-Minimum superheating is required. (the applied pressure helps mould filling and there is no need for high superheating which is normally used for increasing fluidity). This low superheating causes a): increased mould life time, b): refined microstructure, c): less gas porosity and less energy consumption. 5-The air gap between the mould and the solidifying component is eliminated, causing maximum heat transfer rate. Therefore less segregation and refined microstructure is obtained. 6- The applied pressure increases the liquidus temperature of the alloy, ( usually 10- 25 ºC for Al alloys), according to Clausius-Clapeyron Equation resulting in the increased supercooling and microstructure refinement.

The Advantages of Squeeze casting for monolithic alloys 7- با استفاده از این روش می توان کامپوزیتهای ذره ای و الیافی را تولید کرد. 8-در این روش می توان مناطقی را به صورت ترجیحی کامپوزیت کرد اعمال فشار خیس شوندگی را بهبود می بخشد.

The Disadvantages of Squeeze Casting for monolithic alloys 1- This technique can only be used for low melting point alloys due to difficulties in sealing the mould and applying pressure at high temperature. 2- The cost of equipments may be high. 3- امکان تغییر فرم قطعه پیش ساخته در اثر فشار وجود دارد 4-ممکن است تلقیح به صورت کامل انجام نشود لذا برای فلزلت با دامنه انجماد کوتاه یا انجماد پوسته ای بهتر است

+ All of the advantages as mentioned before for monolithic alloys The Advantages of Squeeze casting for Discontinuously reinforced composites All of the advantages as mentioned before for monolithic alloys + 1- Improved wettability and interface characteristics . 2- decreased porosity at the ceramic-matrix interface. 3-More uniform distribution of the second phase within the matrix alloy.

متغیرها 1- فشار 2- دمای قالب 3- دمای پیش ساخته (جلوگیری از واکنش های ناخواسته) 4-میزان فوق گداز(100 درجه کافی است)

روش اسپري دوغاب كامپوزيتي Disintegrated Melt Deposition روش اسپري دوغاب كامپوزيتي كه با نام DMD شناخته مي‌شود، براي توليد كامپوزينهاي زمينه فلزي ذره‌اي در حال تحقيق و توسعه مي باشد . در روش اسپري دوغاب كامپوزيتي ابتدا ذرات سراميكي توسط عمل همزدن (مكانيكي يا مغناطيسي) در داخل مذاب فلزي توزيع شده و سپس اين دوغاب توسط دستگاه اسپري به قطراتي تبديل شده و اين قطرات كامپوزيتي در روي سطح زير لايه رسوب مي كنند حسن اين روش توزيع يكنواخت ذرات در داخل زمينه مي باشد. كامپوزيتهاي توليد شده به اين روش علاوه بر دارا بودن خواص مربوط به مواد سريع منجمد شده (از قبيل ريز دانگي، كاهش جدايش، افزايش حلاليت جامد، خواص تيكسوتروپيك و...)، داراي توزيع كاملاً يكنواختي از ذرات در زمينه و استكام مناسب در فصل مشترك ذرات/ زمينه هستند و اين دو عامل تعيين كننده خواص مكانيكي نهائي مي باشند.

Disintegrated Melt Deposition (DMD) روش اسپري دوغاب كامپوزيتي

Direct incorporation of ceramic particles into the semisolid alloy COMPOCASTING When the particles (or whiskers or short fibers) are added to the slurry in the semisolid state and then it is stirred in the semisolid condition it is called COMPOCASTING.

Before we continue with compocasting let’s have a brief explanation about semisolid processing of the alloys. In 1972, when Spenser (The PhD student of Flemings at MIT) was working on hot tearing of Sn-Pb alloys he designed a device to measure the viscosity of semisolid alloys. This device consisted of two co-axial cylinders in which the semisolid alloy was poured in the gap between them. By rotating the external cylinder, and measuring the rotation speed of the internal one the viscosity was obtained. He realized that by increasing the rotation speed, the viscosity decreased, after stopping the cylinder for a short time, the viscosity increased rapidly. They developed a casting technique in the semisolid state and called it RHEOCASTING.

COMPOCASTING There are two variations of compocasting as follows: Direct incorporation of ceramic particles into the semisolid alloy COMPOCASTING There are two variations of compocasting as follows: 1- The particles are added to the slurry in the semisolid state and then it is heated to above the liquidus temperature of the alloy and cast. This technique is called SL or Semisolid-Liquid method. 2- The particles are added to the slurry in the semisolid state and then it is cast. This technique is called SS or Semisolid-Semisolid method. These techniques vary from the Liquid-Liquid (LL) method which was explained before as the VORTEX or STIR CASTING technique.

THE ADVANTAGES OF COMPOCASTING (IN THE MIXING STAGE) 1-The presence of the primary solid phase in the viscous semi-solid imposes an abrasive action on clumps of undispersed reinforcement in the slurry which assists the incorporation of the ceramic particles. 2-The solidified metallic particles also prevent the non-metallics from settling, floating or agglomerating, resulting in a more homogeneous particle distribution as compared with a fully molten alloy.

The benefits of the SS method The benefits of the SS with respect to the LL and/or SL methods are: (i) lower operating temperatures (lack of superheat) as well as a lower latent heat which result in a longer die life together with a reduced chemical attack of the reinforcement by alloy; (ii) laminar flow of the viscous semi-solid materials; (iii)reduced solidification shrinkage; (iv)lower tendency for hot tearing; (v) supression of segregation, settling or agglomeration and (vi)faster process cycles. These advantages are acompanied with a globular, non-dendritic structure of the solid phase which then explains the thixotropic behaviour of the material.

The Disadvantages of the SS method The major drawbacks of the SS process are porosity, processing difficulties due to high viscosity and requirement for a stringent control on the processing parameters(i.e., temperature and shear rate) to produce defect-free castings with uniform particle distribution.