【摘要】：金屬材料的形核一般與過冷度有著密切的聯(lián)系,保證一定的過冷度需要使模具材料具有很好的傳熱性能,但是由于氣體裹陷現(xiàn)象的存在,使金屬液與模壁之間夾雜了一部分空氣,導(dǎo)致金屬液的傳熱性能變差,使金屬的異質(zhì)形核受到影響。氣體裹陷存在的原因主要是由于模具表面存在一定的微觀粗糙度,當(dāng)金屬液與模具表面接觸時(shí),凹槽部分被密封了空氣,形成了Cassie潤(rùn)濕模型所述的現(xiàn)象,阻礙金屬液與模具表面的接觸,降低了金屬液冷卻過程中對(duì)外界的傳熱效率,同時(shí),這種金屬液與模壁形成潤(rùn)濕體系,因此可以發(fā)現(xiàn)金屬材料表面的潤(rùn)濕性對(duì)于金屬形核起著舉足輕重的作用。本文以金屬液的異質(zhì)形核為出發(fā)點(diǎn),結(jié)合楊氏方程、Wenzel模型理論與Cassie模型理論,以水為介質(zhì)研究金屬表面的潤(rùn)濕性。實(shí)驗(yàn)的第一部分主要采用易于制備試樣的純鋁和高純鋁材料,通過化學(xué)刻蝕的方法制備具有親水性的表面,并在室溫下進(jìn)行時(shí)效,分析潤(rùn)濕性隨時(shí)效時(shí)間的變化規(guī)律。實(shí)驗(yàn)以2mol/L濃度的鹽酸進(jìn)行刻蝕,將試樣分別刻蝕4min到20min,清洗并吹干制備好的試樣,利用OCA15EC接觸角測(cè)量?jī)x進(jìn)行潤(rùn)濕角測(cè)定,然后將試樣放置在室溫下進(jìn)行時(shí)效,并記錄時(shí)效后的潤(rùn)濕角,分析潤(rùn)濕角的變化規(guī)律;采用掃描電子顯微鏡觀察試樣表面的微觀形貌,結(jié)合Wenzel理論與Cassie理論分析潤(rùn)濕角變化的原因;對(duì)試樣做EDS分析,分析時(shí)效后試樣所含元素含量的變化情況,闡述潤(rùn)濕性變化的機(jī)理。第二部分將制備好的試樣在高溫爐中進(jìn)行200℃,300℃和400℃高溫時(shí)效,時(shí)效時(shí)間均為1h,記錄時(shí)效前后的潤(rùn)濕角度,分析潤(rùn)濕角的變化規(guī)律;觀察試樣表面的微觀形貌,分析EDS中的元素變化情況,闡述潤(rùn)濕性變化的機(jī)理。最終得出不同的刻蝕時(shí)間制備的試樣潤(rùn)濕角存在差異,刻蝕時(shí)間為16min的純鋁能夠獲得比較穩(wěn)定的表面形貌,高純鋁材料在進(jìn)行12min的刻蝕即可得到穩(wěn)定的潤(rùn)濕性,試樣的潤(rùn)濕角維持在12°以下,且形貌較好。高溫時(shí)效后發(fā)現(xiàn),不同的刻蝕時(shí)間制備的試樣經(jīng)過高溫時(shí)效潤(rùn)濕角存在差異,在200℃高溫下時(shí)效1h導(dǎo)致潤(rùn)濕角急劇變大,300℃下時(shí)效1h潤(rùn)濕角開始變小,當(dāng)進(jìn)行400℃時(shí)效1h后試樣變?yōu)槌H水。為了使研究更為充分,利用化學(xué)刻蝕法在抗腐蝕能力強(qiáng)的不銹鋼上制備親水表面,因此第三部分以304不銹鋼為基體材料,以化學(xué)刻蝕為制備方法,研究室溫下與高溫時(shí)效后的潤(rùn)濕角變化情況,發(fā)現(xiàn)室溫時(shí)效后的潤(rùn)濕角變化規(guī)律及高溫時(shí)效后的潤(rùn)濕角規(guī)律與鋁基材料的潤(rùn)濕角變化規(guī)律有相似性,但是由于不同金屬之間的元素親水性不同,兩者之間存在著一定的差異。因此,該論文對(duì)于進(jìn)一步研究高溫下金屬液凝固過程中的潤(rùn)濕性有著重要的意義。
[Abstract]:The nucleation of metal materials is generally closely related to the undercooling degree. To ensure a certain undercooling degree, the mold materials need to have good heat transfer performance, but due to the existence of gas entrapment phenomenon, A part of air is mixed between the liquid metal and the die wall, which leads to the poor heat transfer performance of the liquid metal and affects the heterogeneous nucleation of the metal. The reason for the existence of gas entrapment is mainly due to the existence of a certain degree of microroughness on the surface of the die. When the liquid metal is in contact with the surface of the die, the groove part is sealed with air, forming the phenomenon described in the Cassie wetting model. Hinders the contact between the liquid metal and the surface of the die, reduces the heat transfer efficiency to the outside world in the cooling process of the liquid metal, and forms a wetting system between the liquid metal and the wall of the die. Therefore, it can be found that the wettability of metal material surface plays an important role in metal nucleation. In this paper, based on the heterogeneous nucleation of liquid metal, combined with Yang's equation, Wenzel model theory and Cassie model theory, the wettability of metal surface is studied with water as medium. In the first part of the experiment, pure aluminum and high purity aluminum materials which are easy to prepare samples are used to prepare hydrophilic surfaces by chemical etching. the hydrophilic surfaces are aged at room temperature, and the variation of wettability with aging time is analyzed. The samples were etched with hydrochloric acid of 2mol/L concentration for 20 min, and the samples were cleaned and dried. The wetting angle was measured by OCA15EC contact angle measuring instrument, and then the samples were aged at room temperature. The wetting angle after aging was recorded and the change law of wetting angle was analyzed. Scanning electron microscope (SEM) was used to observe the microstructure of the sample surface, and Wenzel theory and Cassie theory were used to analyze the reasons for the change of wetting angle. The EDS analysis of the sample was carried out, the change of element content in the sample after aging was analyzed, and the mechanism of wettability change was expounded. In the second part, the prepared samples were aged at 200 鈩，

本文編號(hào)：2493308